diff --git a/python/PyQt6/core/auto_generated/geometry/qgsrectangle.sip.in b/python/PyQt6/core/auto_generated/geometry/qgsrectangle.sip.in
index 04122d80871f..d6b61a836026 100644
--- a/python/PyQt6/core/auto_generated/geometry/qgsrectangle.sip.in
+++ b/python/PyQt6/core/auto_generated/geometry/qgsrectangle.sip.in
@@ -389,7 +389,11 @@ the specified ``spacing`` between the grid lines.
 
     SIP_PYOBJECT __repr__();
 %MethodCode
-    QString str = QStringLiteral( "<QgsRectangle: %1>" ).arg( sipCpp->asWktCoordinates() );
+    QString str;
+    if ( sipCpp->isNull() )
+      str = QStringLiteral( "<QgsRectangle()>" );
+    else
+      str = QStringLiteral( "<QgsRectangle: %1>" ).arg( sipCpp->asWktCoordinates() );
     sipRes = PyUnicode_FromString( str.toUtf8().constData() );
 %End
 
diff --git a/python/PyQt6/core/auto_generated/gps/qgsgpsdetector.sip.in b/python/PyQt6/core/auto_generated/gps/qgsgpsdetector.sip.in
index 50011ec27f82..3f4627084ba1 100644
--- a/python/PyQt6/core/auto_generated/gps/qgsgpsdetector.sip.in
+++ b/python/PyQt6/core/auto_generated/gps/qgsgpsdetector.sip.in
@@ -23,11 +23,41 @@ Class to detect the GPS port
 #include "qgsgpsdetector.h"
 %End
   public:
-    QgsGpsDetector( const QString &portName );
+
+
+    QgsGpsDetector( const QString &portName = QString(), bool useUnsafeSignals = true );
+%Docstring
+Constructor for QgsGpsDetector.
+
+If ``portName`` is specified, then only devices from the given port will be scanned. Otherwise
+all connection types will be attempted (including internal GPS devices).
+
+Since QGIS 3.38, the ``useUnsafeSignals`` parameter can be set to ``False`` to avoid emitting the
+dangerous and fragile :py:func:`~QgsGpsDetector.detected` signal. This is highly recommended, but is opt-in to avoid
+breaking stable QGIS 3.x API. If ``useUnsafeSignals`` is set to ``False``, only the safe :py:func:`~QgsGpsDetector.connectionDetected` signal
+will be emitted and clients must manually take ownership of the detected connection via a call
+to :py:func:`~QgsGpsDetector.takeConnection`.
+%End
 
 
     ~QgsGpsDetector();
 
+    QgsGpsConnection *takeConnection() /TransferBack/;
+%Docstring
+Returns the detected GPS connection, and removes it from the detector.
+
+The caller takes ownership of the connection. Only the first call to this
+method following a :py:func:`~QgsGpsDetector.connectionDetected` signal will be able to retrieve the
+detected connection -- subsequent calls will return ``None``.
+
+.. warning::
+
+   Do not call this method if the useUnsafeSignals option in the
+   QgsGpsDetector constructor was set to ``True``.
+
+.. versionadded:: 3.38
+%End
+
     static QList< QPair<QString, QString> > availablePorts();
 
   public slots:
@@ -37,14 +67,28 @@ Class to detect the GPS port
 
   signals:
 
+    void connectionDetected();
+%Docstring
+Emitted when a GPS connection is successfully detected.
+
+Call :py:func:`~QgsGpsDetector.takeConnection` to take ownership of the detected connection.
 
-    void detected( QgsGpsConnection *connection );
+.. versionadded:: 3.38
+%End
+
+ void detected( QgsGpsConnection *connection ) /Deprecated/;
 %Docstring
 Emitted when the GPS connection has been detected. A single connection must listen for this signal and
 immediately take ownership of the ``connection`` object.
+
+.. deprecated::
+   This signal is dangerous and extremely unsafe! It is recommended to instead set the ``useUnsafeSignals`` parameter to ``False`` in the QgsGpsDetector constructor and use the safe :py:func:`~QgsGpsDetector.connectionDetected` signal instead.
 %End
 
     void detectionFailed();
+%Docstring
+Emitted when the detector could not find a valid GPS connection.
+%End
 
 };
 
diff --git a/python/console/console.py b/python/console/console.py
index db96ba844034..ba2d96ba3a74 100644
--- a/python/console/console.py
+++ b/python/console/console.py
@@ -145,8 +145,6 @@ def __init__(self, parent=None):
         QWidget.__init__(self, parent)
         self.setWindowTitle(QCoreApplication.translate("PythonConsole", "Python Console"))
 
-        self.settings = QgsSettings()
-
         self.shell = ShellScintilla(self)
         self.setFocusProxy(self.shell)
         self.shellOut = ShellOutputScintilla(self)
@@ -310,7 +308,7 @@ def __init__(self, parent=None):
         objList = QCoreApplication.translate("PythonConsole", "Object Inspector…")
         self.objectListButton = QAction(self)
         self.objectListButton.setCheckable(True)
-        self.objectListButton.setEnabled(self.settings.value("pythonConsole/enableObjectInsp",
+        self.objectListButton.setEnabled(QgsSettings().value("pythonConsole/enableObjectInsp",
                                                              False, type=bool))
         self.objectListButton.setIcon(QgsApplication.getThemeIcon("console/iconClassBrowserConsole.svg"))
         self.objectListButton.setMenuRole(QAction.PreferencesRole)
@@ -675,7 +673,8 @@ def openScriptFileExtEditor(self):
             QDesktopServices.openUrl(QUrl.fromLocalFile(path))
 
     def openScriptFile(self):
-        lastDirPath = self.settings.value("pythonConsole/lastDirPath", QDir.homePath())
+        settings = QgsSettings()
+        lastDirPath = settings.value("pythonConsole/lastDirPath", QDir.homePath())
         openFileTr = QCoreApplication.translate("PythonConsole", "Open File")
         fileList, selected_filter = QFileDialog.getOpenFileNames(
             self, openFileTr, lastDirPath, "Script file (*.py)")
@@ -691,7 +690,7 @@ def openScriptFile(self):
                     self.tabEditorWidget.newTabEditor(tabName, pyFile)
 
                     lastDirPath = QFileInfo(pyFile).path()
-                    self.settings.setValue("pythonConsole/lastDirPath", pyFile)
+                    settings.setValue("pythonConsole/lastDirPath", pyFile)
                     self.updateTabListScript(pyFile, action='append')
 
     def saveScriptFile(self):
@@ -710,7 +709,7 @@ def saveAsScriptFile(self, index=None):
             index = self.tabEditorWidget.currentIndex()
         if not tabWidget.path:
             fileName = self.tabEditorWidget.tabText(index).replace('*', '') + '.py'
-            folder = self.settings.value("pythonConsole/lastDirPath", QDir.homePath())
+            folder = QgsSettings().value("pythonConsole/lastDirPath", QDir.homePath())
             pathFileName = os.path.join(folder, fileName)
             fileNone = True
         else:
@@ -776,22 +775,24 @@ def updateTabListScript(self, script, action=None):
                 self.tabListScript.append(script)
         else:
             self.tabListScript = []
-        self.settings.setValue("pythonConsole/tabScripts",
+        QgsSettings().setValue("pythonConsole/tabScripts",
                                self.tabListScript)
 
     def saveSettingsConsole(self):
-        self.settings.setValue("pythonConsole/splitterConsole", self.splitter.saveState())
-        self.settings.setValue("pythonConsole/splitterObj", self.splitterObj.saveState())
-        self.settings.setValue("pythonConsole/splitterEditor", self.splitterEditor.saveState())
+        settings = QgsSettings()
+        settings.setValue("pythonConsole/splitterConsole", self.splitter.saveState())
+        settings.setValue("pythonConsole/splitterObj", self.splitterObj.saveState())
+        settings.setValue("pythonConsole/splitterEditor", self.splitterEditor.saveState())
 
         self.shell.writeHistoryFile()
 
     def restoreSettingsConsole(self):
-        storedTabScripts = self.settings.value("pythonConsole/tabScripts", [])
+        settings = QgsSettings()
+        storedTabScripts = settings.value("pythonConsole/tabScripts", [])
         self.tabListScript = storedTabScripts
-        self.splitter.restoreState(self.settings.value("pythonConsole/splitterConsole", QByteArray()))
-        self.splitterEditor.restoreState(self.settings.value("pythonConsole/splitterEditor", QByteArray()))
-        self.splitterObj.restoreState(self.settings.value("pythonConsole/splitterObj", QByteArray()))
+        self.splitter.restoreState(settings.value("pythonConsole/splitterConsole", QByteArray()))
+        self.splitterEditor.restoreState(settings.value("pythonConsole/splitterEditor", QByteArray()))
+        self.splitterObj.restoreState(settings.value("pythonConsole/splitterObj", QByteArray()))
 
 
 if __name__ == '__main__':
diff --git a/python/console/console_editor.py b/python/console/console_editor.py
index 8c20b2792868..3b4d77764b55 100644
--- a/python/console/console_editor.py
+++ b/python/console/console_editor.py
@@ -26,6 +26,7 @@
 import re
 import sys
 import tempfile
+from typing import Optional
 from functools import partial
 from operator import itemgetter
 from pathlib import Path
@@ -60,10 +61,9 @@ class Editor(QgsCodeEditorPython):
     def __init__(self, parent=None):
         super().__init__(parent)
         self.parent = parent
-        self.path = None
+        self.path: Optional[str] = None
         #  recent modification time
         self.lastModified = 0
-        self.settings = QgsSettings()
 
         self.setMinimumHeight(120)
         self.setVerticalScrollBarPolicy(Qt.ScrollBarAsNeeded)
@@ -186,7 +186,7 @@ def contextMenuEvent(self, e):
             redoAction.setEnabled(True)
         if QApplication.clipboard().text():
             pasteAction.setEnabled(True)
-        if self.settings.value("pythonConsole/enableObjectInsp",
+        if QgsSettings().value("pythonConsole/enableObjectInsp",
                                False, type=bool):
             showCodeInspection.setEnabled(True)
         menu.exec_(self.mapToGlobal(e.pos()))
@@ -239,7 +239,7 @@ def objectListEditor(self):
             self.pythonconsole.objectListButton.setChecked(True)
 
     def shareOnGist(self, is_public):
-        ACCESS_TOKEN = self.settings.value("pythonConsole/accessTokenGithub", '', type=QByteArray)
+        ACCESS_TOKEN = QgsSettings().value("pythonConsole/accessTokenGithub", '', type=QByteArray)
         if not ACCESS_TOKEN:
             msg_text = QCoreApplication.translate(
                 'PythonConsole', 'GitHub personal access token must be generated (see Console Options)')
@@ -307,7 +307,7 @@ def createTempFile(self):
         return name
 
     def runScriptCode(self):
-        autoSave = self.settings.value("pythonConsole/autoSaveScript", False, type=bool)
+        autoSave = QgsSettings().value("pythonConsole/autoSaveScript", False, type=bool)
         tabWidget = self.tabwidget.currentWidget()
         filename = tabWidget.path
         msgEditorBlank = QCoreApplication.translate('PythonConsole',
@@ -404,24 +404,23 @@ def loadFile(self, filename, readOnly=False):
         self.setModified(False)
         self.recolor()
 
-    def save(self, filename=None):
+    def save(self, filename: Optional[str] = None):
         if self.isReadOnly():
             return
 
-        if self.pythonconsole.settings.value("pythonConsole/formatOnSave", False, type=bool):
+        if QgsSettings().value("pythonConsole/formatOnSave", False, type=bool):
             self.reformatCode()
 
-        tabwidget = self.tabwidget
-        index = tabwidget.indexOf(self.parent)
+        index = self.tabwidget.indexOf(self.parent)
         if filename:
             self.path = filename
-        if self.path is None:
+        if not self.path:
             saveTr = QCoreApplication.translate('PythonConsole',
                                                 'Python Console: Save file')
-            folder = self.pythonconsole.settings.value("pythonConsole/lastDirPath", QDir.homePath())
+            folder = QgsSettings().value("pythonConsole/lastDirPath", QDir.homePath())
             self.path, filter = QFileDialog().getSaveFileName(self,
                                                               saveTr,
-                                                              os.path.join(folder, tabwidget.tabText(index).replace('*', '') + '.py'),
+                                                              os.path.join(folder, self.tabwidget.tabText(index).replace('*', '') + '.py'),
                                                               "Script file (*.py)")
             # If the user didn't select a file, abort the save operation
             if not self.path:
@@ -436,15 +435,15 @@ def save(self, filename=None):
         # Need to use newline='' to avoid adding extra \r characters on Windows
         with open(self.path, 'w', encoding='utf-8', newline='') as f:
             f.write(self.text())
-        tabwidget.setTabTitle(index, Path(self.path).name)
-        tabwidget.setTabToolTip(index, self.path)
+        self.tabwidget.setTabTitle(index, Path(self.path).name)
+        self.tabwidget.setTabToolTip(index, self.path)
         self.setModified(False)
         self.pythonconsole.saveFileButton.setEnabled(False)
         self.lastModified = QFileInfo(self.path).lastModified()
         self.pythonconsole.updateTabListScript(self.path, action='append')
-        tabwidget.listObject(self.parent)
-        lastDirPath = str(Path(self.path).parent)
-        self.pythonconsole.settings.setValue("pythonConsole/lastDirPath", lastDirPath)
+        self.tabwidget.listObject(self.parent)
+        QgsSettings().setValue("pythonConsole/lastDirPath",
+                               Path(self.path).parent.as_posix())
 
     def event(self, e):
         """ Used to override the Application shortcuts when the editor has focus """
@@ -553,8 +552,6 @@ def __init__(self, parent):
         super().__init__(parent=None)
         self.parent = parent
 
-        self.settings = QgsSettings()
-
         self.idx = -1
         # Layout for top frame (restore tabs)
         self.layoutTopFrame = QGridLayout(self)
@@ -641,7 +638,7 @@ def __init__(self, parent):
         self.newTabButton.clicked.connect(self.newTabEditor)
 
     def _currentWidgetChanged(self, tab):
-        if self.settings.value("pythonConsole/enableObjectInsp",
+        if QgsSettings().value("pythonConsole/enableObjectInsp",
                                False, type=bool):
             self.listObject(tab)
         self.changeLastDirPath(tab)
@@ -788,7 +785,7 @@ def restoreTabsOrAddNew(self):
         Restore tabs if they are found in the settings. If none are found it will add a new empty tab.
         """
         # Restore scripts from the previous session
-        tabScripts = self.settings.value("pythonConsole/tabScripts", [])
+        tabScripts = QgsSettings().value("pythonConsole/tabScripts", [])
         self.restoreTabList = tabScripts
 
         if self.restoreTabList:
@@ -911,7 +908,7 @@ def listObject(self, tab):
                     self.parent.listClassMethod.addTopLevelItem(msgItem)
 
     def refreshSettingsEditor(self):
-        objInspectorEnabled = self.settings.value("pythonConsole/enableObjectInsp",
+        objInspectorEnabled = QgsSettings().value("pythonConsole/enableObjectInsp",
                                                   False, type=bool)
         listObj = self.parent.objectListButton
         if self.parent.listClassMethod.isVisible():
@@ -926,7 +923,8 @@ def refreshSettingsEditor(self):
     def changeLastDirPath(self, tab):
         tabWidget = self.widget(tab)
         if tabWidget and tabWidget.path:
-            self.settings.setValue("pythonConsole/lastDirPath", tabWidget.path)
+            QgsSettings().setValue("pythonConsole/lastDirPath",
+                                   Path(tabWidget.path).parent.as_posix())
 
     def showMessage(self, text, level=Qgis.Info, timeout=-1, title=""):
         currWidget = self.currentWidget()
diff --git a/python/console/console_output.py b/python/console/console_output.py
index cd5c3b513c21..d3e3a71552ff 100644
--- a/python/console/console_output.py
+++ b/python/console/console_output.py
@@ -54,7 +54,7 @@ def write(self, m):
 
         if self.style == "_traceback":
             # Show errors in red
-            stderrColor = QColor(self.sO.settings.value("pythonConsole/stderrFontColor", QColor(self.ERROR_COLOR)))
+            stderrColor = QColor(QgsSettings().value("pythonConsole/stderrFontColor", QColor(self.ERROR_COLOR)))
             self.sO.SendScintilla(QsciScintilla.SCI_STYLESETFORE, 0o01, stderrColor)
             self.sO.SendScintilla(QsciScintilla.SCI_STYLESETITALIC, 0o01, True)
             self.sO.SendScintilla(QsciScintilla.SCI_STYLESETBOLD, 0o01, True)
@@ -122,8 +122,6 @@ def __init__(self, parent=None):
         self.parent = parent
         self.shell = self.parent.shell
 
-        self.settings = QgsSettings()
-
         # Creates layout for message bar
         self.layout = QGridLayout(self)
         self.layout.setContentsMargins(0, 0, 0, 0)
diff --git a/python/console/console_sci.py b/python/console/console_sci.py
index 9f9034a59c96..7ce92310a553 100644
--- a/python/console/console_sci.py
+++ b/python/console/console_sci.py
@@ -288,8 +288,6 @@ def __init__(self, parent=None):
         self.opening = ['(', '{', '[', "'", '"']
         self.closing = [')', '}', ']', "'", '"']
 
-        self.settings = QgsSettings()
-
         self.setHistoryFilePath(
             os.path.join(QgsApplication.qgisSettingsDirPath(), "console_history.txt"))
 
diff --git a/python/core/auto_generated/geometry/qgsrectangle.sip.in b/python/core/auto_generated/geometry/qgsrectangle.sip.in
index 04122d80871f..d6b61a836026 100644
--- a/python/core/auto_generated/geometry/qgsrectangle.sip.in
+++ b/python/core/auto_generated/geometry/qgsrectangle.sip.in
@@ -389,7 +389,11 @@ the specified ``spacing`` between the grid lines.
 
     SIP_PYOBJECT __repr__();
 %MethodCode
-    QString str = QStringLiteral( "<QgsRectangle: %1>" ).arg( sipCpp->asWktCoordinates() );
+    QString str;
+    if ( sipCpp->isNull() )
+      str = QStringLiteral( "<QgsRectangle()>" );
+    else
+      str = QStringLiteral( "<QgsRectangle: %1>" ).arg( sipCpp->asWktCoordinates() );
     sipRes = PyUnicode_FromString( str.toUtf8().constData() );
 %End
 
diff --git a/python/core/auto_generated/gps/qgsgpsdetector.sip.in b/python/core/auto_generated/gps/qgsgpsdetector.sip.in
index 50011ec27f82..3f4627084ba1 100644
--- a/python/core/auto_generated/gps/qgsgpsdetector.sip.in
+++ b/python/core/auto_generated/gps/qgsgpsdetector.sip.in
@@ -23,11 +23,41 @@ Class to detect the GPS port
 #include "qgsgpsdetector.h"
 %End
   public:
-    QgsGpsDetector( const QString &portName );
+
+
+    QgsGpsDetector( const QString &portName = QString(), bool useUnsafeSignals = true );
+%Docstring
+Constructor for QgsGpsDetector.
+
+If ``portName`` is specified, then only devices from the given port will be scanned. Otherwise
+all connection types will be attempted (including internal GPS devices).
+
+Since QGIS 3.38, the ``useUnsafeSignals`` parameter can be set to ``False`` to avoid emitting the
+dangerous and fragile :py:func:`~QgsGpsDetector.detected` signal. This is highly recommended, but is opt-in to avoid
+breaking stable QGIS 3.x API. If ``useUnsafeSignals`` is set to ``False``, only the safe :py:func:`~QgsGpsDetector.connectionDetected` signal
+will be emitted and clients must manually take ownership of the detected connection via a call
+to :py:func:`~QgsGpsDetector.takeConnection`.
+%End
 
 
     ~QgsGpsDetector();
 
+    QgsGpsConnection *takeConnection() /TransferBack/;
+%Docstring
+Returns the detected GPS connection, and removes it from the detector.
+
+The caller takes ownership of the connection. Only the first call to this
+method following a :py:func:`~QgsGpsDetector.connectionDetected` signal will be able to retrieve the
+detected connection -- subsequent calls will return ``None``.
+
+.. warning::
+
+   Do not call this method if the useUnsafeSignals option in the
+   QgsGpsDetector constructor was set to ``True``.
+
+.. versionadded:: 3.38
+%End
+
     static QList< QPair<QString, QString> > availablePorts();
 
   public slots:
@@ -37,14 +67,28 @@ Class to detect the GPS port
 
   signals:
 
+    void connectionDetected();
+%Docstring
+Emitted when a GPS connection is successfully detected.
+
+Call :py:func:`~QgsGpsDetector.takeConnection` to take ownership of the detected connection.
 
-    void detected( QgsGpsConnection *connection );
+.. versionadded:: 3.38
+%End
+
+ void detected( QgsGpsConnection *connection ) /Deprecated/;
 %Docstring
 Emitted when the GPS connection has been detected. A single connection must listen for this signal and
 immediately take ownership of the ``connection`` object.
+
+.. deprecated::
+   This signal is dangerous and extremely unsafe! It is recommended to instead set the ``useUnsafeSignals`` parameter to ``False`` in the QgsGpsDetector constructor and use the safe :py:func:`~QgsGpsDetector.connectionDetected` signal instead.
 %End
 
     void detectionFailed();
+%Docstring
+Emitted when the detector could not find a valid GPS connection.
+%End
 
 };
 
diff --git a/python/plugins/processing/algs/qgis/CheckValidity.py b/python/plugins/processing/algs/qgis/CheckValidity.py
index 855662bb40d0..e5220f88faa9 100644
--- a/python/plugins/processing/algs/qgis/CheckValidity.py
+++ b/python/plugins/processing/algs/qgis/CheckValidity.py
@@ -44,7 +44,7 @@
                        QgsProcessingParameterBoolean)
 from processing.algs.qgis.QgisAlgorithm import QgisAlgorithm
 
-settings_method_key = "/qgis/digitizing/validate_geometries"
+settings_method_key = "/digitizing/validate-geometries"
 pluginPath = os.path.split(os.path.split(os.path.dirname(__file__))[0])[0]
 
 
diff --git a/python/plugins/processing/algs/qgis/RandomPointsAlongLines.py b/python/plugins/processing/algs/qgis/RandomPointsAlongLines.py
index 2ddfae8fd2a5..6fdb5d5b9c3a 100644
--- a/python/plugins/processing/algs/qgis/RandomPointsAlongLines.py
+++ b/python/plugins/processing/algs/qgis/RandomPointsAlongLines.py
@@ -100,7 +100,6 @@ def processAlgorithm(self, parameters, context, feedback):
         nPoints = 0
         nIterations = 0
         maxIterations = pointCount * 200
-        featureCount = source.featureCount()
         total = 100.0 / pointCount if pointCount else 1
 
         index = QgsSpatialIndex()
@@ -116,14 +115,22 @@ def processAlgorithm(self, parameters, context, feedback):
 
         ids = source.allFeatureIds()
 
-        while nIterations < maxIterations and nPoints < pointCount:
+        while ids and nIterations < maxIterations and nPoints < pointCount:
             if feedback.isCanceled():
                 break
 
             # pick random feature
             fid = random.choice(ids)
-            f = next(source.getFeatures(request.setFilterFid(fid).setSubsetOfAttributes([])))
+            try:
+                f = next(source.getFeatures(request.setFilterFid(fid).setSubsetOfAttributes([])))
+            except StopIteration:
+                ids.remove(fid)
+                continue
+
             fGeom = f.geometry()
+            if fGeom.isEmpty():
+                ids.remove(fid)
+                continue
 
             if fGeom.isMultipart():
                 lines = fGeom.asMultiPolyline()
@@ -134,13 +141,20 @@ def processAlgorithm(self, parameters, context, feedback):
                 vertices = fGeom.asPolyline()
 
             # pick random segment
-            if len(vertices) == 2:
+            nVertices = len(vertices)
+            if nVertices < 2:
+                nIterations += 1
+                continue
+            if nVertices == 2:
                 vid = 0
             else:
-                vid = random.randint(0, len(vertices) - 2)
+                vid = random.randint(0, nVertices - 2)
             startPoint = vertices[vid]
             endPoint = vertices[vid + 1]
             length = da.measureLine(startPoint, endPoint)
+            if length == 0:
+                nIterations += 1
+                continue
             dist = length * random.random()
 
             d = dist / (length - dist)
diff --git a/python/plugins/processing/tests/AlgorithmsTestBase.py b/python/plugins/processing/tests/AlgorithmsTestBase.py
index d192abe6889b..4a97db068a68 100644
--- a/python/plugins/processing/tests/AlgorithmsTestBase.py
+++ b/python/plugins/processing/tests/AlgorithmsTestBase.py
@@ -168,6 +168,12 @@ def check_algorithm(self, name, defs):
         # ignore user setting for invalid geometry handling
         context = QgsProcessingContext()
         context.setProject(QgsProject.instance())
+        if 'ellipsoid' in defs:
+            # depending on the project settings, we can't always rely
+            # on QgsProject.ellipsoid() returning the same ellipsoid as was
+            # specified in the test definition. So just force ensure that the
+            # context's ellipsoid is the desired one
+            context.setEllipsoid(defs['ellipsoid'])
 
         if 'skipInvalid' in defs and defs['skipInvalid']:
             context.setInvalidGeometryCheck(QgsFeatureRequest.GeometrySkipInvalid)
diff --git a/python/plugins/processing/tests/testdata/qgis_algorithm_tests2.yaml b/python/plugins/processing/tests/testdata/qgis_algorithm_tests2.yaml
index f43816b277bc..d98d5b180628 100644
--- a/python/plugins/processing/tests/testdata/qgis_algorithm_tests2.yaml
+++ b/python/plugins/processing/tests/testdata/qgis_algorithm_tests2.yaml
@@ -1808,6 +1808,7 @@ tests:
 
   - algorithm: native:shortestpathpointtopoint
     name: Shortest path (point to point, shortest route)
+    ellipsoid: WGS84
     params:
       DEFAULT_DIRECTION: 2
       DEFAULT_SPEED: 5.0
@@ -1838,6 +1839,7 @@ tests:
 
   - algorithm: native:shortestpathpointtopoint
     name: Shortest path (point to point, fastest route)
+    ellipsoid: WGS84
     params:
       DEFAULT_DIRECTION: 2
       DEFAULT_SPEED: 5.0
@@ -1869,6 +1871,7 @@ tests:
 
   - algorithm: native:shortestpathlayertopoint
     name: Shortest path layer to point
+    ellipsoid: WGS84
     params:
       DEFAULT_DIRECTION: 2
       DEFAULT_SPEED: 5.0
@@ -1899,6 +1902,7 @@ tests:
 
   - algorithm: native:shortestpathpointtolayer
     name: Shortest path point to layer
+    ellipsoid: WGS84
     params:
       DEFAULT_DIRECTION: 2
       DEFAULT_SPEED: 5.0
@@ -1929,6 +1933,7 @@ tests:
 
   - algorithm: native:serviceareafrompoint
     name: Service area from point (shortest, nodes)
+    ellipsoid: WGS84
     params:
       DEFAULT_DIRECTION: 2
       DEFAULT_SPEED: 50.0
@@ -1960,6 +1965,7 @@ tests:
 
   - algorithm: native:serviceareafrompoint
     name: Service area from point (shortest, nodes, bounds)
+    ellipsoid: WGS84
     params:
       DEFAULT_DIRECTION: 2
       DEFAULT_SPEED: 50.0
@@ -1986,6 +1992,7 @@ tests:
 
   - algorithm: native:serviceareafrompoint
     name: Service area from point (shortest, lines)
+    ellipsoid: WGS84
     params:
       DEFAULT_DIRECTION: 2
       DEFAULT_SPEED: 50.0
@@ -2017,6 +2024,7 @@ tests:
 
   - algorithm: native:serviceareafrompoint
     name: Service area from point (fastest, old parameter)
+    ellipsoid: WGS84
     params:
       DEFAULT_DIRECTION: 2
       DEFAULT_SPEED: 50.0
@@ -2051,6 +2059,7 @@ tests:
 
   - algorithm: native:serviceareafrompoint
     name: Service area from point (fastest, new parameter)
+    ellipsoid: WGS84
     params:
       DEFAULT_DIRECTION: 2
       DEFAULT_SPEED: 50.0
@@ -2085,6 +2094,7 @@ tests:
 
   - algorithm: native:serviceareafromlayer
     name: Service area from layer (shortest, nodes)
+    ellipsoid: WGS84
     params:
       DEFAULT_DIRECTION: 2
       DEFAULT_SPEED: 50.0
@@ -2120,6 +2130,7 @@ tests:
 
   - algorithm: native:serviceareafromlayer
     name: Service area from layer (shortest, nodes, boundary)
+    ellipsoid: WGS84
     params:
       DEFAULT_DIRECTION: 2
       DEFAULT_SPEED: 50.0
@@ -2147,6 +2158,7 @@ tests:
 
   - algorithm: native:serviceareafromlayer
     name: Service area from layer (shortest, lines)
+    ellipsoid: WGS84
     params:
       DEFAULT_DIRECTION: 2
       DEFAULT_SPEED: 50.0
diff --git a/python/pyplugin_installer/installer_data.py b/python/pyplugin_installer/installer_data.py
index a8af38edda86..e4be813f430e 100644
--- a/python/pyplugin_installer/installer_data.py
+++ b/python/pyplugin_installer/installer_data.py
@@ -386,8 +386,8 @@ def xmlDownloaded(self):
                         "plugin_id": plugin_id,
                         "name": pluginNodes.item(i).toElement().attribute("name"),
                         "version_available": version,
-                        "version_available_stable": version if not experimental else "",
-                        "version_available_experimental": version if experimental else "",
+                        "version_available_stable": normalizeVersion(version) if not experimental else "",
+                        "version_available_experimental": normalizeVersion(version) if experimental else "",
                         "description": pluginNodes.item(i).firstChildElement("description").text().strip(),
                         "about": pluginNodes.item(i).firstChildElement("about").text().strip(),
                         "author_name": pluginNodes.item(i).firstChildElement("author_name").text().strip(),
diff --git a/src/3d/qgsshadowrenderingframegraph.cpp b/src/3d/qgsshadowrenderingframegraph.cpp
index 70e49e5da83e..83b8d5e34a51 100644
--- a/src/3d/qgsshadowrenderingframegraph.cpp
+++ b/src/3d/qgsshadowrenderingframegraph.cpp
@@ -186,10 +186,8 @@ Qt3DRender::QFrameGraphNode *QgsShadowRenderingFrameGraph::constructForwardRende
     transparentObjectsRenderStateSet->addRenderState( blendEquation );
 
     Qt3DRender::QBlendEquationArguments *blenEquationArgs = new Qt3DRender::QBlendEquationArguments;
-    blenEquationArgs->setSourceRgb( Qt3DRender::QBlendEquationArguments::Blending::One );
-    blenEquationArgs->setDestinationRgb( Qt3DRender::QBlendEquationArguments::Blending::OneMinusSource1Alpha );
-    blenEquationArgs->setSourceAlpha( Qt3DRender::QBlendEquationArguments::Blending::One );
-    blenEquationArgs->setDestinationAlpha( Qt3DRender::QBlendEquationArguments::Blending::OneMinusSource1Alpha );
+    blenEquationArgs->setSourceRgb( Qt3DRender::QBlendEquationArguments::Blending::SourceAlpha );
+    blenEquationArgs->setDestinationRgb( Qt3DRender::QBlendEquationArguments::Blending::OneMinusSourceAlpha );
     transparentObjectsRenderStateSet->addRenderState( blenEquationArgs );
   }
 
diff --git a/src/analysis/processing/qgsalgorithmnetworkanalysisbase.cpp b/src/analysis/processing/qgsalgorithmnetworkanalysisbase.cpp
index 1aac17581aa0..d273671fc8c0 100644
--- a/src/analysis/processing/qgsalgorithmnetworkanalysisbase.cpp
+++ b/src/analysis/processing/qgsalgorithmnetworkanalysisbase.cpp
@@ -133,7 +133,7 @@ void QgsNetworkAnalysisAlgorithmBase::loadCommonParams( const QVariantMap &param
     mDirector->addStrategy( new QgsNetworkDistanceStrategy() );
   }
 
-  mBuilder = std::make_unique< QgsGraphBuilder >( mNetwork->sourceCrs(), true, tolerance );
+  mBuilder = std::make_unique< QgsGraphBuilder >( mNetwork->sourceCrs(), true, tolerance, context.ellipsoid() );
 }
 
 void QgsNetworkAnalysisAlgorithmBase::loadPoints( QgsFeatureSource *source, QVector< QgsPointXY > &points, QHash< int, QgsAttributes > &attributes, QgsProcessingContext &context, QgsProcessingFeedback *feedback )
diff --git a/src/app/gps/qgsappgpsconnection.cpp b/src/app/gps/qgsappgpsconnection.cpp
index db5b692f355d..cc94879c574f 100644
--- a/src/app/gps/qgsappgpsconnection.cpp
+++ b/src/app/gps/qgsappgpsconnection.cpp
@@ -25,7 +25,6 @@
 #include "qgssettingsentryimpl.h"
 #include "qgssettingsentryenumflag.h"
 
-
 QgsAppGpsConnection::QgsAppGpsConnection( QObject *parent )
   : QObject( parent )
 {
@@ -57,7 +56,7 @@ void QgsAppGpsConnection::setConnection( QgsGpsConnection *connection )
     disconnectGps();
   }
 
-  onConnected( connection );
+  setConnectionPrivate( connection );
 }
 
 QgsPoint QgsAppGpsConnection::lastValidLocation() const
@@ -154,10 +153,13 @@ void QgsAppGpsConnection::connectGps()
   QgisApp::instance()->statusBarIface()->clearMessage();
   showStatusBarMessage( tr( "Connecting to GPS device %1…" ).arg( port ) );
 
-  QgsGpsDetector *detector = new QgsGpsDetector( port );
-  connect( detector, static_cast < void ( QgsGpsDetector::* )( QgsGpsConnection * ) > ( &QgsGpsDetector::detected ), this, &QgsAppGpsConnection::onConnected );
-  connect( detector, &QgsGpsDetector::detectionFailed, this, &QgsAppGpsConnection::onTimeOut );
-  detector->advance();   // start the detection process
+  QgsDebugMsgLevel( QStringLiteral( "Firing up GPS detector" ), 2 );
+
+  // note -- QgsGpsDetector internally uses deleteLater to clean itself up!
+  mDetector = new QgsGpsDetector( port, false );
+  connect( mDetector, &QgsGpsDetector::connectionDetected, this, &QgsAppGpsConnection::onConnectionDetected );
+  connect( mDetector, &QgsGpsDetector::detectionFailed, this, &QgsAppGpsConnection::onTimeOut );
+  mDetector->advance();   // start the detection process
 }
 
 void QgsAppGpsConnection::disconnectGps()
@@ -179,6 +181,10 @@ void QgsAppGpsConnection::disconnectGps()
 
 void QgsAppGpsConnection::onTimeOut()
 {
+  if ( sender() != mDetector )
+    return;
+
+  QgsDebugMsgLevel( QStringLiteral( "GPS detector reported timeout" ), 2 );
   disconnectGps();
   emit connectionTimedOut();
 
@@ -186,9 +192,18 @@ void QgsAppGpsConnection::onTimeOut()
   showGpsConnectFailureWarning( tr( "TIMEOUT - Failed to connect to GPS device." ) );
 }
 
-void QgsAppGpsConnection::onConnected( QgsGpsConnection *conn )
+void QgsAppGpsConnection::onConnectionDetected()
+{
+  if ( sender() != mDetector )
+    return;
+
+  QgsDebugMsgLevel( QStringLiteral( "GPS detector GOT a connection" ), 2 );
+  setConnectionPrivate( mDetector->takeConnection() );
+}
+
+void QgsAppGpsConnection::setConnectionPrivate( QgsGpsConnection *connection )
 {
-  mConnection = conn;
+  mConnection = connection;
   connect( mConnection, &QgsGpsConnection::stateChanged, this, &QgsAppGpsConnection::stateChanged );
   connect( mConnection, &QgsGpsConnection::nmeaSentenceReceived, this, &QgsAppGpsConnection::nmeaSentenceReceived );
   connect( mConnection, &QgsGpsConnection::fixStatusChanged, this, &QgsAppGpsConnection::fixStatusChanged );
diff --git a/src/app/gps/qgsappgpsconnection.h b/src/app/gps/qgsappgpsconnection.h
index 9c82af42853f..7b992c8cfeb2 100644
--- a/src/app/gps/qgsappgpsconnection.h
+++ b/src/app/gps/qgsappgpsconnection.h
@@ -25,6 +25,7 @@ class QgsGpsConnection;
 class QgsGpsInformation;
 class QgsPoint;
 class QgsMessageBarItem;
+class QgsGpsDetector;
 
 /**
  * Manages a single "canonical" GPS connection for use in the QGIS app, eg for displaying GPS
@@ -140,8 +141,9 @@ class APP_EXPORT QgsAppGpsConnection : public QObject
   private slots:
 
     void onTimeOut();
+    void onConnectionDetected();
 
-    void onConnected( QgsGpsConnection *conn );
+    void setConnectionPrivate( QgsGpsConnection *connection );
 
   private:
 
@@ -150,6 +152,7 @@ class APP_EXPORT QgsAppGpsConnection : public QObject
     void showGpsConnectFailureWarning( const QString &message );
     void showMessage( Qgis::MessageLevel level, const QString &message );
 
+    QPointer< QgsGpsDetector > mDetector;
     QgsGpsConnection *mConnection = nullptr;
     QPointer< QgsMessageBarItem > mConnectionMessageItem;
 };
diff --git a/src/app/qgsidentifyresultsdialog.cpp b/src/app/qgsidentifyresultsdialog.cpp
index 90f022923e43..81ff2ef18d1d 100644
--- a/src/app/qgsidentifyresultsdialog.cpp
+++ b/src/app/qgsidentifyresultsdialog.cpp
@@ -354,6 +354,8 @@ QgsIdentifyResultsDialog::QgsIdentifyResultsDialog( QgsMapCanvas *canvas, QWidge
 
   mOpenFormAction->setDisabled( true );
 
+  lstResults->setVerticalScrollMode( QListView::ScrollMode::ScrollPerPixel );
+
   QgsSettings mySettings;
   mDock = new QgsDockWidget( tr( "Identify Results" ), QgisApp::instance() );
   mDock->setObjectName( QStringLiteral( "IdentifyResultsDock" ) );
diff --git a/src/core/browser/qgsdirectoryitem.cpp b/src/core/browser/qgsdirectoryitem.cpp
index 746c4d462aca..629a38056947 100644
--- a/src/core/browser/qgsdirectoryitem.cpp
+++ b/src/core/browser/qgsdirectoryitem.cpp
@@ -59,6 +59,10 @@ void QgsDirectoryItem::init( const QString &dirName )
 
   QgsSettings settings;
 
+  const QFileInfo fi { mDirPath };
+  mIsDir = fi.isDir();
+  mIsSymLink = fi.isSymLink();
+
   mMonitoring = monitoringForPath( mDirPath );
   switch ( mMonitoring )
   {
@@ -165,8 +169,7 @@ QIcon QgsDirectoryItem::icon()
     return QgsDataItem::icon();
 
   // symbolic link? use link icon
-  const QFileInfo fi( mDirPath );
-  if ( fi.isDir() && fi.isSymLink() )
+  if ( mIsDir && mIsSymLink )
   {
     return mIconColor.isValid()
            ? QgsApplication::getThemeIcon( QStringLiteral( "/mIconFolderLinkParams.svg" ), mIconColor, mIconColor.darker() )
@@ -452,7 +455,9 @@ bool QgsDirectoryItem::pathShouldByMonitoredByDefault( const QString &path )
 
   // else if we know that the path is on a slow device, we don't monitor by default
   // as this can be very expensive and slow down QGIS
-  if ( QgsFileUtils::pathIsSlowDevice( path ) )
+  // Add trailing slash or windows API functions like GetDriveTypeW won't identify
+  // UNC network drives correctly
+  if ( QgsFileUtils::pathIsSlowDevice( path.endsWith( '/' ) ? path : path + '/' ) )
     return false;
 
   // paths are monitored by default if no explicit setting is in place, and the user hasn't
diff --git a/src/core/browser/qgsdirectoryitem.h b/src/core/browser/qgsdirectoryitem.h
index 0334624e5031..3b5fe960d516 100644
--- a/src/core/browser/qgsdirectoryitem.h
+++ b/src/core/browser/qgsdirectoryitem.h
@@ -216,6 +216,9 @@ class CORE_EXPORT QgsDirectoryItem : public QgsDataCollectionItem
     QDateTime mLastScan;
     QColor mIconColor;
 
+    bool mIsDir = false;
+    bool mIsSymLink = false;
+
     friend class TestQgsDataItem;
 };
 
diff --git a/src/core/geometry/qgsgeometrycollection.cpp b/src/core/geometry/qgsgeometrycollection.cpp
index 029b0c47bad8..1bd3dd723ac6 100644
--- a/src/core/geometry/qgsgeometrycollection.cpp
+++ b/src/core/geometry/qgsgeometrycollection.cpp
@@ -908,7 +908,7 @@ bool QgsGeometryCollection::isValid( QString &error, Qgis::GeometryValidityFlags
     return error.isEmpty();
   }
 
-  QgsGeos geos( this );
+  QgsGeos geos( this, /* precision = */ 0, /* allowInvalidSubGeom = */ false );
   bool res = geos.isValid( &error, flags & Qgis::GeometryValidityFlag::AllowSelfTouchingHoles, nullptr );
   if ( flags == 0 )
   {
diff --git a/src/core/geometry/qgsgeos.cpp b/src/core/geometry/qgsgeos.cpp
index 22db5ced5573..f2492478c838 100644
--- a/src/core/geometry/qgsgeos.cpp
+++ b/src/core/geometry/qgsgeos.cpp
@@ -139,12 +139,12 @@ void geos::GeosDeleter::operator()( GEOSCoordSequence *sequence ) const
 ///@endcond
 
 
-QgsGeos::QgsGeos( const QgsAbstractGeometry *geometry, double precision )
+QgsGeos::QgsGeos( const QgsAbstractGeometry *geometry, double precision, bool allowInvalidSubGeom )
   : QgsGeometryEngine( geometry )
   , mGeos( nullptr )
   , mPrecision( precision )
 {
-  cacheGeos();
+  cacheGeos( allowInvalidSubGeom );
 }
 
 QgsGeometry QgsGeos::geometryFromGeos( GEOSGeometry *geos )
@@ -246,7 +246,7 @@ void QgsGeos::geometryChanged()
 {
   mGeos.reset();
   mGeosPrepared.reset();
-  cacheGeos();
+  cacheGeos( false );
 }
 
 void QgsGeos::prepareGeometry()
@@ -262,7 +262,7 @@ void QgsGeos::prepareGeometry()
   }
 }
 
-void QgsGeos::cacheGeos() const
+void QgsGeos::cacheGeos( bool allowInvalidSubGeom ) const
 {
   if ( mGeos )
   {
@@ -274,7 +274,7 @@ void QgsGeos::cacheGeos() const
     return;
   }
 
-  mGeos = asGeos( mGeometry, mPrecision );
+  mGeos = asGeos( mGeometry, mPrecision, allowInvalidSubGeom );
 }
 
 QgsAbstractGeometry *QgsGeos::intersection( const QgsAbstractGeometry *geom, QString *errorMsg, const QgsGeometryParameters &parameters ) const
@@ -1624,7 +1624,7 @@ QgsPoint QgsGeos::coordSeqPoint( const GEOSCoordSequence *cs, int i, bool hasZ,
   return QgsPoint( t, x, y, z, m );
 }
 
-geos::unique_ptr QgsGeos::asGeos( const QgsAbstractGeometry *geom, double precision )
+geos::unique_ptr QgsGeos::asGeos( const QgsAbstractGeometry *geom, double precision, bool allowInvalidSubGeom )
 {
   if ( !geom )
     return nullptr;
@@ -1675,6 +1675,14 @@ geos::unique_ptr QgsGeos::asGeos( const QgsAbstractGeometry *geom, double precis
     for ( int i = 0; i < c->numGeometries(); ++i )
     {
       geomVector[i] = asGeos( c->geometryN( i ), precision ).release();
+      if ( !allowInvalidSubGeom && !geomVector[i] )
+      {
+        for ( int j = 0; j < i; ++j )
+        {
+          GEOSGeom_destroy_r( geosinit()->ctxt, geomVector[j] );
+        }
+        return nullptr;
+      }
     }
     return createGeosCollection( geosType, geomVector );
   }
diff --git a/src/core/geometry/qgsgeos.h b/src/core/geometry/qgsgeos.h
index 062f4730fc43..a47010ae531b 100644
--- a/src/core/geometry/qgsgeos.h
+++ b/src/core/geometry/qgsgeos.h
@@ -103,8 +103,9 @@ class CORE_EXPORT QgsGeos: public QgsGeometryEngine
      * GEOS geometry engine constructor
      * \param geometry The geometry
      * \param precision The precision of the grid to which to snap the geometry vertices. If 0, no snapping is performed.
+     * \param allowInvalidSubGeom Whether invalid sub-geometries should be skipped without error (since QGIS 3.38)
      */
-    QgsGeos( const QgsAbstractGeometry *geometry, double precision = 0 );
+    QgsGeos( const QgsAbstractGeometry *geometry, double precision = 0, bool allowInvalidSubGeom = true );
 
     /**
      * Creates a new QgsGeometry object, feeding in a geometry in GEOS format.
@@ -608,8 +609,9 @@ class CORE_EXPORT QgsGeos: public QgsGeometryEngine
      * Returns a geos geometry - caller takes ownership of the object (should be deleted with GEOSGeom_destroy_r)
      * \param geometry geometry to convert to GEOS representation
      * \param precision The precision of the grid to which to snap the geometry vertices. If 0, no snapping is performed.
+     * \param allowInvalidSubGeom Whether invalid sub-geometries should be skipped without error (since QGIS 3.38)
      */
-    static geos::unique_ptr asGeos( const QgsAbstractGeometry *geometry, double precision = 0 );
+    static geos::unique_ptr asGeos( const QgsAbstractGeometry *geometry, double precision = 0, bool allowInvalidSubGeom = true );
     static QgsPoint coordSeqPoint( const GEOSCoordSequence *cs, int i, bool hasZ, bool hasM );
 
     static GEOSContextHandle_t getGEOSHandler();
@@ -640,7 +642,7 @@ class CORE_EXPORT QgsGeos: public QgsGeometryEngine
     };
 
     //geos util functions
-    void cacheGeos() const;
+    void cacheGeos( bool allowInvalidSubGeom ) const;
 
     /**
      * Returns a geometry representing the overlay operation with \a geom.
diff --git a/src/core/geometry/qgsrectangle.h b/src/core/geometry/qgsrectangle.h
index f78be34aa062..a88ad9fef475 100644
--- a/src/core/geometry/qgsrectangle.h
+++ b/src/core/geometry/qgsrectangle.h
@@ -641,7 +641,11 @@ class CORE_EXPORT QgsRectangle
 #ifdef SIP_RUN
     SIP_PYOBJECT __repr__();
     % MethodCode
-    QString str = QStringLiteral( "<QgsRectangle: %1>" ).arg( sipCpp->asWktCoordinates() );
+    QString str;
+    if ( sipCpp->isNull() )
+      str = QStringLiteral( "<QgsRectangle()>" );
+    else
+      str = QStringLiteral( "<QgsRectangle: %1>" ).arg( sipCpp->asWktCoordinates() );
     sipRes = PyUnicode_FromString( str.toUtf8().constData() );
     % End
 #endif
diff --git a/src/core/gps/qgsgpsdetector.cpp b/src/core/gps/qgsgpsdetector.cpp
index b78de32e686c..3317ff88b8c1 100644
--- a/src/core/gps/qgsgpsdetector.cpp
+++ b/src/core/gps/qgsgpsdetector.cpp
@@ -21,7 +21,7 @@
 #include "qgsgpsdconnection.h"
 #include "qgssettingstree.h"
 #include "qgssettingsentryenumflag.h"
-
+#include "qgslogger.h"
 
 #if defined(QT_POSITIONING_LIB)
 #include "qgsqtlocationconnection.h"
@@ -64,7 +64,8 @@ QList< QPair<QString, QString> > QgsGpsDetector::availablePorts()
   return devs;
 }
 
-QgsGpsDetector::QgsGpsDetector( const QString &portName )
+QgsGpsDetector::QgsGpsDetector( const QString &portName, bool useUnsafeSignals )
+  : mUseUnsafeSignals( useUnsafeSignals )
 {
 #if defined( HAVE_QTSERIALPORT )
   mBaudList << QSerialPort::Baud4800 << QSerialPort::Baud9600 << QSerialPort::Baud38400 << QSerialPort::Baud57600 << QSerialPort::Baud115200;  //add 57600 for SXBlueII GPS unit
@@ -72,19 +73,63 @@ QgsGpsDetector::QgsGpsDetector( const QString &portName )
 
   if ( portName.isEmpty() )
   {
+    QgsDebugMsgLevel( QStringLiteral( "Attempting to autodetect GPS connection" ), 2 );
     mPortList = availablePorts();
   }
   else
   {
+    QgsDebugMsgLevel( QStringLiteral( "Attempting GPS connection for %1" ).arg( portName ), 2 );
     mPortList << QPair<QString, QString>( portName, portName );
   }
+
+  mTimeoutTimer = new QTimer( this );
+  mTimeoutTimer->setSingleShot( true );
+  connect( mTimeoutTimer, &QTimer::timeout, this, &QgsGpsDetector::connectionTimeout );
+}
+
+QgsGpsDetector::~QgsGpsDetector()
+{
+  QgsDebugMsgLevel( QStringLiteral( "Destroying GPS detector" ), 2 );
 }
 
-QgsGpsDetector::~QgsGpsDetector() = default;
+QgsGpsConnection *QgsGpsDetector::takeConnection()
+{
+  if ( mUseUnsafeSignals )
+  {
+    QgsDebugError( QStringLiteral( "QgsGpsDetector::takeConnection() incorrectly called when useUnsafeSignals option is in effect" ) );
+    return nullptr;
+  }
+
+  if ( mConn )
+  {
+    // this is NOT the detectors connection anymore, so disconnect all signals from the connection
+    // to the detector so that there's no unwanted interaction with the detector
+    mConn->disconnect( this );
+  }
+
+#ifdef QGISDEBUG
+  if ( mConn )
+  {
+    QgsDebugMsgLevel( QStringLiteral( "Detected GPS connection is being taken by caller" ), 2 );
+  }
+  else
+  {
+    QgsDebugError( QStringLiteral( "Something is trying to take the GPS connection, but it doesn't exist!" ) );
+  }
+#endif
+
+  return mConn.release();
+}
 
 void QgsGpsDetector::advance()
 {
-  mConn.reset();
+  if ( mConn )
+  {
+    QgsDebugMsgLevel( QStringLiteral( "Destroying existing connection to attempt next configuration combination" ), 2 );
+    mConn.reset();
+  }
+
+  QgsDebugMsgLevel( QStringLiteral( "Trying to find a connection..." ), 2 );
 
   while ( !mConn )
   {
@@ -97,11 +142,14 @@ void QgsGpsDetector::advance()
 
     if ( mPortIndex == mPortList.size() )
     {
+      QgsDebugError( QStringLiteral( "No more devices to try!" ) );
       emit detectionFailed();
       deleteLater();
       return;
     }
 
+    QgsDebugMsgLevel( QStringLiteral( "Attempting connection to device %1 @ %2" ).arg( mPortIndex ).arg( mBaudIndex ), 2 );
+
     if ( mPortList.at( mPortIndex ).first.contains( ':' ) )
     {
       mBaudIndex = mBaudList.size() - 1;
@@ -109,14 +157,17 @@ void QgsGpsDetector::advance()
       QStringList gpsParams = mPortList.at( mPortIndex ).first.split( ':' );
 
       Q_ASSERT( gpsParams.size() >= 3 );
+      QgsDebugMsgLevel( QStringLiteral( "Connecting to GPSD device %1" ).arg( gpsParams.join( ',' ) ), 2 );
 
       mConn = std::make_unique< QgsGpsdConnection >( gpsParams[0], gpsParams[1].toShort(), gpsParams[2] );
     }
     else if ( mPortList.at( mPortIndex ).first.contains( QLatin1String( "internalGPS" ) ) )
     {
 #if defined(QT_POSITIONING_LIB)
+      QgsDebugMsgLevel( QStringLiteral( "Connecting to QtLocation service device" ), 2 );
       mConn = std::make_unique< QgsQtLocationConnection >();
 #else
+      QgsDebugError( QStringLiteral( "QT_POSITIONING_LIB not found and mPortList matches internalGPS, this should never happen" ) );
       qWarning( "QT_POSITIONING_LIB not found and mPortList matches internalGPS, this should never happen" );
 #endif
     }
@@ -132,45 +183,94 @@ void QgsGpsDetector::advance()
       serial->setDataBits( QgsGpsDetector::settingsGpsDataBits->value() );
       serial->setStopBits( QgsGpsDetector::settingsGpsStopBits->value() );
 
+      QgsDebugMsgLevel( QStringLiteral( "Connecting to serial GPS device %1 (@ %2)" ).arg( mPortList.at( mPortIndex ).first ).arg( mBaudList[ mBaudIndex ] ), 2 );
+
       if ( serial->open( QIODevice::ReadOnly ) )
       {
+        QgsDebugMsgLevel( QStringLiteral( "Successfully opened, have a port connection ready" ), 2 );
         mConn = std::make_unique< QgsNmeaConnection >( serial.release() );
       }
+      else
+      {
+        QgsDebugError( QStringLiteral( "Serial port could NOT be opened" ) );
+      }
 #else
+      QgsDebugError( QStringLiteral( "QT5SERIALPORT not found and mPortList matches serial port, this should never happen" ) );
       qWarning( "QT5SERIALPORT not found and mPortList matches serial port, this should never happen" );
 #endif
     }
+
+    if ( !mConn )
+    {
+      QgsDebugError( QStringLiteral( "Got to end of connection handling loop, but have no connection!" ) );
+    }
   }
 
-  connect( mConn.get(), &QgsGpsConnection::stateChanged, this, static_cast < void ( QgsGpsDetector::* )( const QgsGpsInformation & ) >( &QgsGpsDetector::detected ) );
-  connect( mConn.get(), &QObject::destroyed, this, &QgsGpsDetector::connDestroyed );
+  QgsDebugMsgLevel( QStringLiteral( "Have a connection, now listening for messages" ), 2 );
+
+  connect( mConn.get(), &QgsGpsConnection::stateChanged, this, qOverload< const QgsGpsInformation & >( &QgsGpsDetector::detected ) );
+  if ( mUseUnsafeSignals )
+  {
+    connect( mConn.get(), &QObject::destroyed, this, &QgsGpsDetector::connDestroyed );
+  }
 
   // leave 2s to pickup a valid string
-  QTimer::singleShot( 2000, this, &QgsGpsDetector::advance );
+  mTimeoutTimer->start( 2000 );
 }
 
-void QgsGpsDetector::detected( const QgsGpsInformation &info )
+void QgsGpsDetector::detected( const QgsGpsInformation & )
 {
-  Q_UNUSED( info )
+  QgsDebugMsgLevel( QStringLiteral( "Detected information" ), 2 );
 
   if ( !mConn )
   {
+    mTimeoutTimer->stop();
+
     // advance if connection was destroyed
+    QgsDebugError( QStringLiteral( "Got information, but CONNECTION WAS DESTROYED EXTERNALLY!" ) );
     advance();
   }
   else if ( mConn->status() == QgsGpsConnection::GPSDataReceived )
   {
+    mTimeoutTimer->stop();
+    // stop listening for state changed signals, we've already validated this connection and don't want subsequent calls
+    // to QgsGpsDetector::detected being made
+    disconnect( mConn.get(), &QgsGpsConnection::stateChanged, this, qOverload< const QgsGpsInformation & >( &QgsGpsDetector::detected ) );
+
     // signal detected
+    QgsDebugMsgLevel( QStringLiteral( "Connection status IS GPSDataReceived" ), 2 );
 
-    // let's hope there's a single, unique connection to this signal... otherwise... boom
-    emit detected( mConn.release() );
+    if ( mUseUnsafeSignals )
+    {
+      // let's hope there's a single, unique connection to this signal... otherwise... boom!
+      Q_NOWARN_DEPRECATED_PUSH
+      emit detected( mConn.release() );
+      Q_NOWARN_DEPRECATED_POP
+    }
+    else
+    {
+      emit connectionDetected();
+    }
 
     deleteLater();
   }
+  else
+  {
+    // don't stop timeout, we keep waiting to see if later we get the desired connection status...
+    QgsDebugMsgLevel( QStringLiteral( "Connection status is NOT GPSDataReceived. It is %1" ).arg( mConn->status() ), 2 );
+  }
+}
+
+void QgsGpsDetector::connectionTimeout()
+{
+  QgsDebugMsgLevel( QStringLiteral( "No data received within max listening time" ), 2 );
+  advance();
 }
 
 void QgsGpsDetector::connDestroyed( QObject *obj )
 {
+  QgsDebugError( QStringLiteral( "CONNECTION WAS DESTROYED EXTERNALLY!" ) );
+
   // WTF? This whole class needs re-writing...
   if ( obj == mConn.get() )
   {
diff --git a/src/core/gps/qgsgpsdetector.h b/src/core/gps/qgsgpsdetector.h
index 90712a301334..59c9971ba6e1 100644
--- a/src/core/gps/qgsgpsdetector.h
+++ b/src/core/gps/qgsgpsdetector.h
@@ -38,6 +38,7 @@ class QgsSettingsEntryEnumFlag;
 
 class QgsGpsConnection;
 class QgsGpsInformation;
+class QTimer;
 
 /**
  * \ingroup core
@@ -47,7 +48,22 @@ class CORE_EXPORT QgsGpsDetector : public QObject
 {
     Q_OBJECT
   public:
-    QgsGpsDetector( const QString &portName );
+
+    // TODO QGIS 4.0 -- remove useUnsafeSignals option
+
+    /**
+     * Constructor for QgsGpsDetector.
+     *
+     * If \a portName is specified, then only devices from the given port will be scanned. Otherwise
+     * all connection types will be attempted (including internal GPS devices).
+     *
+     * Since QGIS 3.38, the \a useUnsafeSignals parameter can be set to FALSE to avoid emitting the
+     * dangerous and fragile detected() signal. This is highly recommended, but is opt-in to avoid
+     * breaking stable QGIS 3.x API. If \a useUnsafeSignals is set to FALSE, only the safe connectionDetected() signal
+     * will be emitted and clients must manually take ownership of the detected connection via a call
+     * to takeConnection().
+     */
+    QgsGpsDetector( const QString &portName = QString(), bool useUnsafeSignals = true );
 
 #if defined( HAVE_QTSERIALPORT )
     static const QgsSettingsEntryEnumFlag<QSerialPort::StopBits> *settingsGpsStopBits SIP_SKIP;
@@ -58,6 +74,20 @@ class CORE_EXPORT QgsGpsDetector : public QObject
 
     ~QgsGpsDetector() override;
 
+    /**
+     * Returns the detected GPS connection, and removes it from the detector.
+     *
+     * The caller takes ownership of the connection. Only the first call to this
+     * method following a connectionDetected() signal will be able to retrieve the
+     * detected connection -- subsequent calls will return NULLPTR.
+     *
+     * \warning Do not call this method if the useUnsafeSignals option in the
+     * QgsGpsDetector constructor was set to TRUE.
+     *
+     * \since QGIS 3.38
+     */
+    QgsGpsConnection *takeConnection() SIP_TRANSFERBACK;
+
     static QList< QPair<QString, QString> > availablePorts();
 
   public slots:
@@ -67,24 +97,41 @@ class CORE_EXPORT QgsGpsDetector : public QObject
 
   signals:
 
-    // TODO QGIS 4.0 - this is horrible, fragile, leaky and crash prone API.
-    // don't transfer ownership with this signal, and add an explicit takeConnection member!
+    /**
+     * Emitted when a GPS connection is successfully detected.
+     *
+     * Call takeConnection() to take ownership of the detected connection.
+     *
+     * \since QGIS 3.38
+     */
+    void connectionDetected();
 
     /**
      * Emitted when the GPS connection has been detected. A single connection must listen for this signal and
      * immediately take ownership of the \a connection object.
+     *
+     * \deprecated This signal is dangerous and extremely unsafe! It is recommended to instead set the \a useUnsafeSignals parameter to FALSE in the QgsGpsDetector constructor and use the safe connectionDetected() signal instead.
      */
-    void detected( QgsGpsConnection *connection );
+    Q_DECL_DEPRECATED void detected( QgsGpsConnection *connection ) SIP_DEPRECATED;
 
+    /**
+     * Emitted when the detector could not find a valid GPS connection.
+     */
     void detectionFailed();
 
+  private slots:
+
+    void connectionTimeout();
+
   private:
+    bool mUseUnsafeSignals = true;
     int mPortIndex = 0;
     int mBaudIndex = -1;
     QList< QPair< QString, QString > > mPortList;
     QList<qint32> mBaudList;
 
     std::unique_ptr< QgsGpsConnection > mConn;
+    QTimer *mTimeoutTimer = nullptr;
 };
 
 #endif // QGSGPSDETECTOR_H
diff --git a/src/core/gps/qgsnmeaconnection.cpp b/src/core/gps/qgsnmeaconnection.cpp
index 4460f7c684d8..72dc8fc7cb39 100644
--- a/src/core/gps/qgsnmeaconnection.cpp
+++ b/src/core/gps/qgsnmeaconnection.cpp
@@ -60,15 +60,24 @@ void QgsNmeaConnection::parseData()
 
   if ( numBytes >= 6 )
   {
+    QgsDebugMsgLevel( QStringLiteral( "Got %1 NMEA bytes" ).arg( numBytes ), 3 );
+    QgsDebugMsgLevel( QStringLiteral( "Current NMEA device status is %1" ).arg( mStatus ), 3 );
     if ( mStatus != GPSDataReceived )
     {
+      QgsDebugMsgLevel( QStringLiteral( "Setting device status to DataReceived" ), 3 );
       mStatus = DataReceived;
     }
 
     //append new data to the remaining results from last parseData() call
     mStringBuffer.append( mSource->read( numBytes ) );
     processStringBuffer();
-    emit stateChanged( mLastGPSInformation );
+    QgsDebugMsgLevel( QStringLiteral( "Processed buffer" ), 3 );
+
+    QgsDebugMsgLevel( QStringLiteral( "New status is %1" ).arg( mStatus ), 3 );
+    if ( mStatus == GPSDataReceived )
+    {
+      emit stateChanged( mLastGPSInformation );
+    }
   }
 }
 
diff --git a/src/core/layertree/qgslayertreemodel.cpp b/src/core/layertree/qgslayertreemodel.cpp
index 6766cfd2fec7..c1824aea4b0a 100644
--- a/src/core/layertree/qgslayertreemodel.cpp
+++ b/src/core/layertree/qgslayertreemodel.cpp
@@ -41,7 +41,10 @@ QgsLayerTreeModel::QgsLayerTreeModel( QgsLayerTree *rootNode, QObject *parent )
   , mRootNode( rootNode )
   , mFlags( ShowLegend | AllowLegendChangeState | DeferredLegendInvalidation )
 {
-  connectToRootNode();
+  if ( rootNode )
+  {
+    connectToRootNode();
+  }
 
   mFontLayer.setBold( true );
 
@@ -1072,9 +1075,11 @@ void QgsLayerTreeModel::connectToRootNode()
 
 void QgsLayerTreeModel::disconnectFromRootNode()
 {
-  disconnect( mRootNode, nullptr, this, nullptr );
-
-  disconnectFromLayers( mRootNode );
+  if ( mRootNode )
+  {
+    disconnect( mRootNode, nullptr, this, nullptr );
+    disconnectFromLayers( mRootNode );
+  }
 }
 
 void QgsLayerTreeModel::recursivelyEmitDataChanged( const QModelIndex &idx )
diff --git a/src/core/layout/qgslayoutitemlegend.cpp b/src/core/layout/qgslayoutitemlegend.cpp
index 3ed55d97dcb3..cd6a3dcb8cc3 100644
--- a/src/core/layout/qgslayoutitemlegend.cpp
+++ b/src/core/layout/qgslayoutitemlegend.cpp
@@ -46,7 +46,7 @@
 
 QgsLayoutItemLegend::QgsLayoutItemLegend( QgsLayout *layout )
   : QgsLayoutItem( layout )
-  , mLegendModel( new QgsLegendModel( layout->project()->layerTreeRoot(), this ) )
+  , mLegendModel( new QgsLegendModel( nullptr, this ) )
 {
 #if 0 //no longer required?
   connect( &layout->atlasComposition(), &QgsAtlasComposition::renderEnded, this, &QgsLayoutItemLegend::onAtlasEnded );
@@ -105,6 +105,8 @@ void QgsLayoutItemLegend::paint( QPainter *painter, const QStyleOptionGraphicsIt
   if ( !painter )
     return;
 
+  ensureModelIsInitialized();
+
   if ( mFilterAskedForUpdate )
   {
     mFilterAskedForUpdate = false;
@@ -309,11 +311,28 @@ bool QgsLayoutItemLegend::resizeToContents() const
 
 void QgsLayoutItemLegend::setCustomLayerTree( QgsLayerTree *rootGroup )
 {
-  mLegendModel->setRootGroup( rootGroup ? rootGroup : ( mLayout ? mLayout->project()->layerTreeRoot() : nullptr ) );
+  if ( !mDeferLegendModelInitialization )
+  {
+    mLegendModel->setRootGroup( rootGroup ? rootGroup : ( mLayout ? mLayout->project()->layerTreeRoot() : nullptr ) );
+  }
 
   mCustomLayerTree.reset( rootGroup );
 }
 
+void QgsLayoutItemLegend::ensureModelIsInitialized()
+{
+  if ( mDeferLegendModelInitialization )
+  {
+    mDeferLegendModelInitialization = false;
+    setCustomLayerTree( mCustomLayerTree.release() );
+  }
+}
+
+QgsLegendModel *QgsLayoutItemLegend::model()
+{
+  ensureModelIsInitialized();
+  return mLegendModel.get();
+}
 
 void QgsLayoutItemLegend::setAutoUpdateModel( bool autoUpdate )
 {
@@ -1020,7 +1039,10 @@ void QgsLayoutItemLegend::clearLegendCachedData()
     }
   };
 
-  clearNodeCache( mLegendModel->rootGroup() );
+  if ( QgsLayerTree *rootGroup = mLegendModel->rootGroup() )
+  {
+    clearNodeCache( rootGroup );
+  }
 }
 
 void QgsLayoutItemLegend::mapLayerStyleOverridesChanged()
diff --git a/src/core/layout/qgslayoutitemlegend.h b/src/core/layout/qgslayoutitemlegend.h
index 39d7410f595b..ee1b6c275a3e 100644
--- a/src/core/layout/qgslayoutitemlegend.h
+++ b/src/core/layout/qgslayoutitemlegend.h
@@ -23,7 +23,7 @@
 #include "qgslayoutitem.h"
 #include "qgslayertreemodel.h"
 #include "qgslegendsettings.h"
-#include "qgslayertreegroup.h"
+#include "qgslayertree.h"
 #include "qgsexpressioncontext.h"
 
 class QgsLayerTreeModel;
@@ -158,7 +158,7 @@ class CORE_EXPORT QgsLayoutItemLegend : public QgsLayoutItem
     /**
      * Returns the legend model.
      */
-    QgsLegendModel *model() { return mLegendModel.get(); }
+    QgsLegendModel *model();
 
     /**
      * Sets whether the legend content should auto update to reflect changes in the project's
@@ -636,8 +636,10 @@ class CORE_EXPORT QgsLayoutItemLegend : public QgsLayoutItem
 
     void setModelStyleOverrides( const QMap<QString, QString> &overrides );
 
+    void ensureModelIsInitialized();
     std::unique_ptr< QgsLegendModel > mLegendModel;
-    std::unique_ptr< QgsLayerTreeGroup > mCustomLayerTree;
+    std::unique_ptr< QgsLayerTree > mCustomLayerTree;
+    bool mDeferLegendModelInitialization = true;
 
     QgsLegendSettings mSettings;
 
diff --git a/src/core/network/qgsnetworkaccessmanager.cpp b/src/core/network/qgsnetworkaccessmanager.cpp
index 4ab2e97fee22..cf297b32101e 100644
--- a/src/core/network/qgsnetworkaccessmanager.cpp
+++ b/src/core/network/qgsnetworkaccessmanager.cpp
@@ -216,6 +216,8 @@ QgsNetworkAccessManager::QgsNetworkAccessManager( QObject *parent )
 {
   setProxyFactory( new QgsNetworkProxyFactory() );
   setCookieJar( new QgsNetworkCookieJar( this ) );
+  enableStrictTransportSecurityStore( true );
+  setStrictTransportSecurityEnabled( true );
 }
 
 void QgsNetworkAccessManager::setSslErrorHandler( std::unique_ptr<QgsSslErrorHandler> handler )
diff --git a/src/core/providers/ogr/qgsogrprovider.cpp b/src/core/providers/ogr/qgsogrprovider.cpp
index 1b7a39481a38..dda333b8f7f2 100644
--- a/src/core/providers/ogr/qgsogrprovider.cpp
+++ b/src/core/providers/ogr/qgsogrprovider.cpp
@@ -1258,8 +1258,8 @@ QVariant QgsOgrProvider::defaultValue( int fieldId ) const
     }
   }
 
-  ( void )mAttributeFields.at( fieldId ).convertCompatible( resultVar );
-  return resultVar;
+  const bool compatible = mAttributeFields.at( fieldId ).convertCompatible( resultVar );
+  return compatible && !QgsVariantUtils::isNull( resultVar ) ? resultVar : QVariant();
 }
 
 QString QgsOgrProvider::defaultValueClause( int fieldIndex ) const
diff --git a/src/core/qgsbookmarkmodel.cpp b/src/core/qgsbookmarkmodel.cpp
index b1a2f04a99e5..cc2ffaaf4d60 100644
--- a/src/core/qgsbookmarkmodel.cpp
+++ b/src/core/qgsbookmarkmodel.cpp
@@ -222,11 +222,9 @@ bool QgsBookmarkManagerModel::setData( const QModelIndex &index, const QVariant
   return false;
 }
 
-bool QgsBookmarkManagerModel::insertRows( int, int count, const QModelIndex &parent )
+bool QgsBookmarkManagerModel::insertRows( int, int count, const QModelIndex & )
 {
   // append
-  const int oldCount = mManager->bookmarks().count();
-  beginInsertRows( parent, oldCount, oldCount + count );
   bool result = true;
   for ( int i = 0; i < count; ++i )
   {
@@ -236,14 +234,11 @@ bool QgsBookmarkManagerModel::insertRows( int, int count, const QModelIndex &par
     mBlocked = false;
     result &= res;
   }
-  endInsertRows();
   return result;
 }
 
-bool QgsBookmarkManagerModel::removeRows( int row, int count, const QModelIndex &parent )
+bool QgsBookmarkManagerModel::removeRows( int row, int count, const QModelIndex & )
 {
-  beginRemoveRows( parent, row, row + count );
-
   const QList< QgsBookmark > appBookmarks = mManager->bookmarks();
   const QList< QgsBookmark > projectBookmarks = mProjectManager->bookmarks();
   for ( int r = row + count - 1; r >= row; --r )
@@ -253,7 +248,6 @@ bool QgsBookmarkManagerModel::removeRows( int row, int count, const QModelIndex
     else
       mManager->removeBookmark( appBookmarks.at( r ).id() );
   }
-  endRemoveRows();
   return true;
 }
 
diff --git a/src/core/raster/qgspalettedrasterrenderer.cpp b/src/core/raster/qgspalettedrasterrenderer.cpp
index f1429d857ca3..e312ede9b441 100644
--- a/src/core/raster/qgspalettedrasterrenderer.cpp
+++ b/src/core/raster/qgspalettedrasterrenderer.cpp
@@ -42,21 +42,33 @@ QgsPalettedRasterRenderer::QgsPalettedRasterRenderer( QgsRasterInterface *input,
   : QgsRasterRenderer( input, QStringLiteral( "paletted" ) )
   , mBand( bandNumber )
 {
+
+  QHash<QString, QHash<QColor, QVector<QVariant>>> classData;
+  // Prepare for the worst case, where we have to store all the values for each class
+  classData.reserve( classes.size() );
+  // This is to keep the ordering of the labels, because hash is fast but unordered
+  QVector<QString> labels;
+  labels.reserve( classes.size() );
+
   for ( const Class &klass : std::as_const( classes ) )
   {
-    MultiValueClassData::iterator it = std::find_if( mMultiValueClassData.begin(), mMultiValueClassData.end(), [&klass]( const MultiValueClass & val ) -> bool
-    {
-      return val.label == klass.label && val.color == klass.color ;
-    } );
-    if ( it != mMultiValueClassData.end() )
+    if ( !classData.contains( klass.label ) )
     {
-      it->values.push_back( klass.value );
+      labels.push_back( klass.label );
     }
-    else
+    classData[klass.label][klass.color].push_back( klass.value );
+  }
+
+  mMultiValueClassData.reserve( classData.size() );
+
+  for ( auto labelIt = labels.constBegin(); labelIt != labels.constEnd(); ++labelIt )
+  {
+    for ( auto colorIt = classData[*labelIt].constBegin(); colorIt != classData[*labelIt].constEnd(); ++colorIt )
     {
-      mMultiValueClassData.push_back( MultiValueClass{ { klass.value }, klass.color, klass.label } );
+      mMultiValueClassData.push_back( MultiValueClass{ colorIt.value(), colorIt.key(), *labelIt } );
     }
   }
+
   updateArrays();
 }
 
diff --git a/src/core/symbology/qgssymbol.cpp b/src/core/symbology/qgssymbol.cpp
index c281f8f9db64..cd5239d537fe 100644
--- a/src/core/symbology/qgssymbol.cpp
+++ b/src/core/symbology/qgssymbol.cpp
@@ -942,7 +942,7 @@ void QgsSymbol::drawPreviewIcon( QPainter *painter, QSize size, QgsRenderContext
   const bool prevForceVector = context->forceVectorOutput();
   context->setForceVectorOutput( true );
 
-  const double opacity = expressionContext ? dataDefinedProperties().valueAsDouble( QgsSymbol::PropertyOpacity, *expressionContext, mOpacity ) : mOpacity;
+  const double opacity = expressionContext ? dataDefinedProperties().valueAsDouble( QgsSymbol::PropertyOpacity, *expressionContext, mOpacity * 100 ) * 0.01 : mOpacity;
 
   QgsSymbolRenderContext symbolContext( *context, Qgis::RenderUnit::Unknown, opacity, false, mRenderHints, nullptr );
   symbolContext.setSelected( selected );
diff --git a/src/core/vector/qgsvectorlayerfeatureiterator.cpp b/src/core/vector/qgsvectorlayerfeatureiterator.cpp
index e1cf3fb8998e..b5374883663c 100644
--- a/src/core/vector/qgsvectorlayerfeatureiterator.cpp
+++ b/src/core/vector/qgsvectorlayerfeatureiterator.cpp
@@ -622,7 +622,7 @@ void QgsVectorLayerFeatureIterator::setInterruptionChecker( QgsFeedback *interru
 
 bool QgsVectorLayerFeatureIterator::isValid() const
 {
-  return mProviderIterator.isValid();
+  return mChangedFeaturesIterator.isValid() || mProviderIterator.isValid();
 }
 
 bool QgsVectorLayerFeatureIterator::fetchNextAddedFeature( QgsFeature &f )
diff --git a/src/gui/qgsmapcanvas.cpp b/src/gui/qgsmapcanvas.cpp
index fc450fd3744f..0f26fbe7457f 100644
--- a/src/gui/qgsmapcanvas.cpp
+++ b/src/gui/qgsmapcanvas.cpp
@@ -48,6 +48,7 @@ email                : sherman at mrcc.com
 #include "qgsapplication.h"
 #include "qgsexception.h"
 #include "qgsfeatureiterator.h"
+#include "qgsgrouplayer.h"
 #include "qgslogger.h"
 #include "qgsmapcanvas.h"
 #include "qgsmapcanvasmap.h"
@@ -1052,6 +1053,21 @@ void QgsMapCanvas::clearTemporalCache()
         if ( !alreadyInvalidatedThisLayer )
           mCache->invalidateCacheForLayer( layer );
       }
+      else if ( QgsGroupLayer *gl = qobject_cast<QgsGroupLayer *>( layer ) )
+      {
+        const QList<QgsMapLayer *> childLayerList = gl->childLayers();
+        for ( QgsMapLayer *childLayer : childLayerList )
+        {
+          if ( childLayer->temporalProperties() && childLayer->temporalProperties()->isActive() )
+          {
+            if ( childLayer->temporalProperties()->flags() & QgsTemporalProperty::FlagDontInvalidateCachedRendersWhenRangeChanges )
+              continue;
+
+            mCache->invalidateCacheForLayer( layer );
+            break;
+          }
+        }
+      }
     }
 
     if ( invalidateLabels )
@@ -1083,6 +1099,21 @@ void QgsMapCanvas::clearElevationCache()
 
         mCache->invalidateCacheForLayer( layer );
       }
+      else if ( QgsGroupLayer *gl = qobject_cast<QgsGroupLayer *>( layer ) )
+      {
+        const QList<QgsMapLayer *> childLayerList = gl->childLayers();
+        for ( QgsMapLayer *childLayer : childLayerList )
+        {
+          if ( childLayer->elevationProperties() && childLayer->elevationProperties()->hasElevation() )
+          {
+            if ( childLayer->elevationProperties()->flags() & QgsMapLayerElevationProperties::FlagDontInvalidateCachedRendersWhenRangeChanges )
+              continue;
+
+            mCache->invalidateCacheForLayer( layer );
+            break;
+          }
+        }
+      }
     }
 
     if ( invalidateLabels )
diff --git a/src/providers/mssql/qgsmssqlprovider.cpp b/src/providers/mssql/qgsmssqlprovider.cpp
index 2aa5af324224..4cf649118868 100644
--- a/src/providers/mssql/qgsmssqlprovider.cpp
+++ b/src/providers/mssql/qgsmssqlprovider.cpp
@@ -21,6 +21,7 @@
 #include "qgsmssqlproviderconnection.h"
 #include "qgsfeedback.h"
 #include "qgsdbquerylog.h"
+#include "qgsvariantutils.h"
 
 #include <QtGlobal>
 #include <QFileInfo>
@@ -685,7 +686,8 @@ QVariant QgsMssqlProvider::defaultValue( int fieldId ) const
     return QVariant();
   }
 
-  return query.value( 0 );
+  const QVariant res = query.value( 0 );
+  return QgsVariantUtils::isNull( res ) ? QVariant() : res;
 }
 
 QString QgsMssqlProvider::storageType() const
diff --git a/src/providers/postgres/qgspostgresconn.h b/src/providers/postgres/qgspostgresconn.h
index 48700a6d8f36..721be1bcd61f 100644
--- a/src/providers/postgres/qgspostgresconn.h
+++ b/src/providers/postgres/qgspostgresconn.h
@@ -318,9 +318,7 @@ class QgsPostgresConn : public QObject
 
     QString uniqueCursorName();
 
-#if 0
     PGconn *pgConnection() { return mConn; }
-#endif
 
     //
     // libpq wrapper
diff --git a/src/providers/postgres/qgspostgreslistener.cpp b/src/providers/postgres/qgspostgreslistener.cpp
index d314b396f4b0..af54f081f897 100644
--- a/src/providers/postgres/qgspostgreslistener.cpp
+++ b/src/providers/postgres/qgspostgreslistener.cpp
@@ -19,6 +19,7 @@
 #include "qgsdatasourceuri.h"
 #include "qgscredentials.h"
 #include "qgslogger.h"
+#include "qgspostgresconn.h"
 
 #ifdef Q_OS_WIN
 #include <winsock.h>
@@ -26,8 +27,6 @@
 #include <sys/select.h>
 #endif
 
-const int PG_CONNECT_TIMEOUT = 30;
-
 extern "C"
 {
 #include <libpq-fe.h>
@@ -37,17 +36,27 @@ std::unique_ptr< QgsPostgresListener > QgsPostgresListener::create( const QStrin
 {
   std::unique_ptr< QgsPostgresListener > res( new QgsPostgresListener( connString ) );
   QgsDebugMsgLevel( QStringLiteral( "starting notification listener" ), 2 );
-  res->start();
-  res->mMutex.lock();
-  res->mIsReadyCondition.wait( &res->mMutex );
-  res->mMutex.unlock();
 
+  res->start();
   return res;
 }
 
 QgsPostgresListener::QgsPostgresListener( const QString &connString )
-  : mConnString( connString )
 {
+  mConn = QgsPostgresConn::connectDb( connString, true, false );
+  if ( mConn )
+  {
+    mConn->moveToThread( this );
+
+    QgsPostgresResult result( mConn->LoggedPQexec( "QgsPostgresListener", QStringLiteral( "LISTEN qgis" ) ) );
+    if ( result.PQresultStatus() != PGRES_COMMAND_OK )
+    {
+      QgsDebugError( QStringLiteral( "error in listen" ) );
+
+      mConn->unref();
+      mConn = nullptr;
+    }
+  }
 }
 
 QgsPostgresListener::~QgsPostgresListener()
@@ -56,73 +65,27 @@ QgsPostgresListener::~QgsPostgresListener()
   QgsDebugMsgLevel( QStringLiteral( "stopping the loop" ), 2 );
   wait();
   QgsDebugMsgLevel( QStringLiteral( "notification listener stopped" ), 2 );
+
+  if ( mConn )
+    mConn->unref();
 }
 
 void QgsPostgresListener::run()
 {
-  PGconn *conn = nullptr;
-  QString connectString = mConnString;
-
-  connectString += QStringLiteral( " connect_timeout=%1" ).arg( PG_CONNECT_TIMEOUT );
-  conn = PQconnectdb( connectString.toUtf8() );
-
-  if ( PQstatus( conn ) != CONNECTION_OK )
-  {
-    QgsDataSourceUri uri( connectString );
-    QString username = uri.username();
-    QString password = uri.password();
-
-    PQfinish( conn );
-
-    QgsCredentials::instance()->lock();
-
-    if ( QgsCredentials::instance()->get( mConnString, username, password, PQerrorMessage( conn ) ) )
-    {
-      uri.setUsername( username );
-      uri.setPassword( password );
-      connectString = uri.connectionInfo( false );
-      connectString += QStringLiteral( " connect_timeout=%1" ).arg( PG_CONNECT_TIMEOUT );
-
-      conn = PQconnectdb( connectString.toUtf8() );
-      if ( PQstatus( conn ) == CONNECTION_OK )
-        QgsCredentials::instance()->put( mConnString, username, password );
-    }
-
-    QgsCredentials::instance()->unlock();
-
-    if ( PQstatus( conn ) != CONNECTION_OK )
-    {
-      PQfinish( conn );
-      QgsDebugMsgLevel( QStringLiteral( "LISTENer not started" ), 2 );
-      return;
-    }
-  }
-
-
-  PGresult *res = PQexec( conn, "LISTEN qgis" );
-  if ( PQresultStatus( res ) != PGRES_COMMAND_OK )
+  if ( !mConn )
   {
     QgsDebugError( QStringLiteral( "error in listen" ) );
-    PQclear( res );
-    PQfinish( conn );
-    mMutex.lock();
-    mIsReadyCondition.wakeOne();
-    mMutex.unlock();
     return;
   }
-  PQclear( res );
-  mMutex.lock();
-  mIsReadyCondition.wakeOne();
-  mMutex.unlock();
 
-  const int sock = PQsocket( conn );
+  const int sock = PQsocket( mConn->pgConnection() );
   if ( sock < 0 )
   {
     QgsDebugError( QStringLiteral( "error in socket" ) );
-    PQfinish( conn );
     return;
   }
 
+  PGconn *pgconn = mConn->pgConnection();
   forever
   {
     fd_set input_mask;
@@ -139,8 +102,8 @@ void QgsPostgresListener::run()
       break;
     }
 
-    PQconsumeInput( conn );
-    PGnotify *n = PQnotifies( conn );
+    PQconsumeInput( pgconn );
+    PGnotify *n = PQnotifies( pgconn );
     if ( n )
     {
       const QString msg( n->extra );
@@ -155,7 +118,4 @@ void QgsPostgresListener::run()
       break;
     }
   }
-  PQfinish( conn );
 }
-
-
diff --git a/src/providers/postgres/qgspostgreslistener.h b/src/providers/postgres/qgspostgreslistener.h
index 9f81386aa7d0..da546407e340 100644
--- a/src/providers/postgres/qgspostgreslistener.h
+++ b/src/providers/postgres/qgspostgreslistener.h
@@ -24,6 +24,9 @@
 #include <QWaitCondition>
 #include <QMutex>
 
+class QgsPostgresConn;
+
+
 /**
  * \class QgsPostgresListener
  * \brief Launch a thread to listen on postgres notifications on the "qgis" channel, the notify signal is emitted on postgres notify.
@@ -52,9 +55,8 @@ class QgsPostgresListener : public QThread
 
   private:
     volatile bool mStop = false;
-    const QString mConnString;
-    QWaitCondition mIsReadyCondition;
-    QMutex mMutex;
+
+    QgsPostgresConn *mConn = nullptr;
 
     QgsPostgresListener( const QString &connString );
 
diff --git a/src/providers/postgres/qgspostgresprovider.cpp b/src/providers/postgres/qgspostgresprovider.cpp
index 6b4a4ecf3d43..e90da5bb68fc 100644
--- a/src/providers/postgres/qgspostgresprovider.cpp
+++ b/src/providers/postgres/qgspostgresprovider.cpp
@@ -1374,7 +1374,7 @@ bool QgsPostgresProvider::loadFields()
                              .arg( quotedValue( mQuery ) )
                              .arg( quotedValue( fieldName ) );
       QgsPostgresResult seqResult( connectionRO()->PQexec( seqSql ) );
-      if ( seqResult.PQntuples() == 1 )
+      if ( seqResult.PQntuples() == 1 && !seqResult.PQgetisnull( 0, 0 ) )
       {
         defValMap[tableoid][attnum] = QStringLiteral( "nextval(%1)" ).arg( quotedValue( seqResult.PQgetvalue( 0, 0 ) ) );
       }
diff --git a/src/providers/spatialite/qgsspatialiteprovider.cpp b/src/providers/spatialite/qgsspatialiteprovider.cpp
index fa4609dca806..ee69772f3292 100644
--- a/src/providers/spatialite/qgsspatialiteprovider.cpp
+++ b/src/providers/spatialite/qgsspatialiteprovider.cpp
@@ -1103,8 +1103,8 @@ QVariant QgsSpatiaLiteProvider::defaultValue( int fieldId ) const
     }
   }
 
-  ( void )mAttributeFields.at( fieldId ).convertCompatible( resultVar );
-  return resultVar;
+  const bool compatible = mAttributeFields.at( fieldId ).convertCompatible( resultVar );
+  return compatible && !QgsVariantUtils::isNull( resultVar ) ? resultVar : QVariant();
 }
 
 QString QgsSpatiaLiteProvider::defaultValueClause( int fieldIndex ) const
diff --git a/src/server/services/wfs/qgswfsgetfeature.cpp b/src/server/services/wfs/qgswfsgetfeature.cpp
index e994491b9e86..d1cec9340a5b 100644
--- a/src/server/services/wfs/qgswfsgetfeature.cpp
+++ b/src/server/services/wfs/qgswfsgetfeature.cpp
@@ -461,7 +461,20 @@ namespace QgsWfs
       {
 
         // For WFS 1.1 we honor requested CRS and axis order
-        const QString srsName {request.serverParameters().value( QStringLiteral( "SRSNAME" ) )};
+        // Axis is not inverted if srsName starts with EPSG
+        // It needs to be an EPSG urn, e.g. urn:ogc:def:crs:EPSG::4326
+        // This follows geoserver convention
+        // See: https://docs.geoserver.org/stable/en/user/services/wfs/axis_order.html
+        // if the crs is defined in the parameters, use it
+        // otherwise:
+        //  - geojson uses 'EPSG:4326' by default
+        //  - other formats use the default CRS (DefaultSRS, which is the layer's CRS)
+        const QString requestSrsName = request.serverParameters().value( QStringLiteral( "SRSNAME" ) );
+        const QString srsName
+        {
+          !requestSrsName.isEmpty() ? requestSrsName :
+          ( aRequest.outputFormat == QgsWfsParameters::Format::GeoJSON ? QStringLiteral( "EPSG:4326" ) : outputCrs.authid() )
+        };
         const bool invertAxis { mWfsParameters.versionAsNumber() >= QgsProjectVersion( 1, 1, 0 ) &&
                                 outputCrs.hasAxisInverted() &&
                                 ! srsName.startsWith( QLatin1String( "EPSG:" ) ) };
@@ -1248,7 +1261,12 @@ namespace QgsWfs
         if ( format == QgsWfsParameters::Format::GML3 )
         {
           // For WFS 1.1 we honor requested CRS and axis order
-          const QString srsName {request.serverParameters().value( QStringLiteral( "SRSNAME" ) )};
+          // Axis is not inverted if srsName starts with EPSG
+          // It needs to be an EPSG urn, e.g. urn:ogc:def:crs:EPSG::4326
+          // This follows geoserver convention
+          // See: https://docs.geoserver.org/stable/en/user/services/wfs/axis_order.html
+          const QString requestSrsName = request.serverParameters().value( QStringLiteral( "SRSNAME" ) );
+          const QString srsName = !requestSrsName.isEmpty() ? requestSrsName : crs.authid();
           const bool invertAxis { mWfsParameters.versionAsNumber() >= QgsProjectVersion( 1, 1, 0 ) &&
                                   crs.hasAxisInverted() &&
                                   ! srsName.startsWith( QLatin1String( "EPSG:" ) ) };
diff --git a/src/server/services/wms/qgswmsrendercontext.cpp b/src/server/services/wms/qgswmsrendercontext.cpp
index 259904771f30..9a86c5873199 100644
--- a/src/server/services/wms/qgswmsrendercontext.cpp
+++ b/src/server/services/wms/qgswmsrendercontext.cpp
@@ -636,6 +636,9 @@ bool QgsWmsRenderContext::isValidWidthHeight() const
 
 bool QgsWmsRenderContext::isValidWidthHeight( int width, int height ) const
 {
+  if ( width <= 0 || height <= 0 )
+    return false;
+
   //test if maxWidth / maxHeight are set in the project or as an env variable
   //and WIDTH / HEIGHT parameter is in the range allowed range
   //WIDTH
@@ -678,14 +681,15 @@ bool QgsWmsRenderContext::isValidWidthHeight( int width, int height ) const
     return false;
   }
 
-  // Sanity check from internal QImage checks (see qimage.cpp)
+  // Sanity check from internal QImage checks
+  // (see QImageData::calculateImageParameters() in qimage_p.h)
   // this is to report a meaningful error message in case of
   // image creation failure and to differentiate it from out
   // of memory conditions.
 
   // depth for now it cannot be anything other than 32, but I don't like
   // to hardcode it: I hope we will support other depths in the future.
-  uint depth = 32;
+  int depth = 32;
   switch ( mParameters.format() )
   {
     case QgsWmsParameters::Format::JPG:
@@ -694,12 +698,12 @@ bool QgsWmsRenderContext::isValidWidthHeight( int width, int height ) const
       depth = 32;
   }
 
+  if ( width > ( std::numeric_limits<int>::max() - 31 ) / depth )
+    return false;
+
   const int bytes_per_line = ( ( width * depth + 31 ) >> 5 ) << 2; // bytes per scanline (must be multiple of 4)
 
-  if ( std::numeric_limits<int>::max() / depth < static_cast<uint>( width )
-       || bytes_per_line <= 0
-       || height <= 0
-       || std::numeric_limits<int>::max() / static_cast<uint>( bytes_per_line ) < static_cast<uint>( height )
+  if ( std::numeric_limits<int>::max() / bytes_per_line < height
        || std::numeric_limits<int>::max() / sizeof( uchar * ) < static_cast<uint>( height ) )
   {
     return false;
diff --git a/tests/src/core/testqgsnmeaconnection.cpp b/tests/src/core/testqgsnmeaconnection.cpp
index 7618f7d97ba2..64feb5a916cf 100644
--- a/tests/src/core/testqgsnmeaconnection.cpp
+++ b/tests/src/core/testqgsnmeaconnection.cpp
@@ -50,6 +50,14 @@ class ReplayNmeaConnection : public QgsNmeaConnection
       return spy.constLast().at( 0 ).value< QgsGpsInformation >();
     }
 
+    void pushString( const QString &string )
+    {
+      const qint64 pos = mBuffer->pos();
+      mBuffer->write( string.toLocal8Bit().constData() );
+      mBuffer->seek( pos );
+      parseData();
+    }
+
   private:
 
     QBuffer *mBuffer = nullptr;
@@ -74,6 +82,7 @@ class TestQgsNmeaConnection : public QgsTest
     void testConstellation();
     void testPosition();
     void testComponent();
+    void testIncompleteMessage();
 
 };
 
@@ -468,5 +477,31 @@ void TestQgsNmeaConnection::testComponent()
   QCOMPARE( info.componentValue( Qgis::GpsInformationComponent::Bearing ).toDouble(), 2 );
 }
 
+void TestQgsNmeaConnection::testIncompleteMessage()
+{
+  ReplayNmeaConnection connection;
+  QSignalSpy stateChangedSpy( &connection, &QgsNmeaConnection::stateChanged );
+
+  QCOMPARE( connection.status(), QgsGpsConnection::Status::Connected );
+
+  // start with an incomplete message
+  connection.pushString( QStringLiteral( "$GPGGA," ) );
+  // status should be "data received", we don't have the full sentence yet
+  QCOMPARE( connection.status(), QgsGpsConnection::Status::DataReceived );
+  // should be no stateChanged signal yet, we are still waiting on more data
+  QCOMPARE( stateChangedSpy.size(), 0 );
+
+  connection.pushString( QStringLiteral( "084112.185,6900.0,N,01800.0,E,1,04,1.4,35.0,M,29.4,M,,0000*63\r\n" ) );
+  // got a full sentence now, status should be "data received"
+  QCOMPARE( connection.status(), QgsGpsConnection::Status::GPSDataReceived );
+  QCOMPARE( stateChangedSpy.size(), 1 );
+  const QgsGpsInformation info = stateChangedSpy.at( 0 ).at( 0 ).value< QgsGpsInformation >();
+
+  QCOMPARE( info.componentValue( Qgis::GpsInformationComponent::Location ).value< QgsPointXY >(), QgsPointXY( 18, 69 ) );
+  QCOMPARE( info.componentValue( Qgis::GpsInformationComponent::Altitude ).toDouble(), 35 );
+  QCOMPARE( info.componentValue( Qgis::GpsInformationComponent::GroundSpeed ).toDouble(), 0 );
+  QCOMPARE( info.componentValue( Qgis::GpsInformationComponent::Bearing ).toDouble(), 0 );
+}
+
 QGSTEST_MAIN( TestQgsNmeaConnection )
 #include "testqgsnmeaconnection.moc"
diff --git a/tests/src/python/test_provider_ogr.py b/tests/src/python/test_provider_ogr.py
index 35db32061cb9..d90d4bd3c875 100644
--- a/tests/src/python/test_provider_ogr.py
+++ b/tests/src/python/test_provider_ogr.py
@@ -1146,8 +1146,7 @@ def testSpatialiteDefaultValues(self):
 
         # Test default values
         dp = vl.dataProvider()
-        # FIXME: should it be None?
-        self.assertTrue(dp.defaultValue(0).isNull())
+        self.assertEqual(dp.defaultValue(0), NULL)
         self.assertIsNone(dp.defaultValue(1))
         # FIXME: This fails because there is no backend-side evaluation in this provider
         # self.assertTrue(dp.defaultValue(2).startswith(now.strftime('%Y-%m-%d')))
diff --git a/tests/src/python/test_provider_postgres.py b/tests/src/python/test_provider_postgres.py
index 6747ab578ce9..428f17c7c086 100644
--- a/tests/src/python/test_provider_postgres.py
+++ b/tests/src/python/test_provider_postgres.py
@@ -2708,6 +2708,40 @@ def testDefaultValuesAndClauses(self):
         self.assertEqual(feature.attribute(4), 123)
         self.assertEqual(feature.attribute(5), 'My default')
 
+    def testNoDefaultValueClauseForPKWithNoDefaultValue(self):
+        """Test issue GH #54058"""
+
+        self.execSQLCommand(
+            'ALTER TABLE IF EXISTS qgis_test."gh_54058" DROP CONSTRAINT IF EXISTS pk_gh_54058;')
+        self.execSQLCommand(
+            'DROP TABLE IF EXISTS qgis_test."gh_54058" CASCADE;')
+        self.execSQLCommand(
+            'CREATE TABLE qgis_test."gh_54058" ( "T_Id" integer NOT NULL, name text );')
+        self.execSQLCommand(
+            'ALTER TABLE qgis_test."gh_54058" ADD CONSTRAINT pk_gh_54058 PRIMARY KEY ("T_Id");')
+
+        vl = QgsVectorLayer(self.dbconn + ' sslmode=disable key=\'id\' table="qgis_test"."gh_54058" () sql=', 'gh_54058', 'postgres')
+        self.assertTrue(vl.isValid())
+
+        dp = vl.dataProvider()
+        self.assertEqual(dp.defaultValueClause(0), '')  # Not nextVal(NULL) anymore!
+
+    def testNoDefaultValueClauseForUniqueNotNullFieldWithNoDefaultValue(self):
+        """Test issue GH #54058b"""
+
+        self.execSQLCommand(
+            'DROP TABLE IF EXISTS qgis_test."gh_54058b" CASCADE;')
+        self.execSQLCommand(
+            'CREATE TABLE qgis_test."gh_54058b" ( "T_Id" integer NOT NULL, name varchar(8) UNIQUE, codigo integer NOT NULL UNIQUE);')
+
+        vl = QgsVectorLayer(self.dbconn + ' sslmode=disable key=\'id\' table="qgis_test"."gh_54058b" () sql=', 'gh_54058b', 'postgres')
+        self.assertTrue(vl.isValid())
+
+        dp = vl.dataProvider()
+        self.assertEqual(dp.defaultValueClause(0), '')  # The issue didn't occur here
+        self.assertEqual(dp.defaultValueClause(1), '')  # The issue didn't occur here
+        self.assertEqual(dp.defaultValueClause(2), '')  # Not nextVal(NULL) anymore!
+
     def testEncodeDecodeUri(self):
         """Test PG encode/decode URI"""
 
diff --git a/tests/src/python/test_provider_spatialite.py b/tests/src/python/test_provider_spatialite.py
index 156d3e357cd4..938185e72abf 100644
--- a/tests/src/python/test_provider_spatialite.py
+++ b/tests/src/python/test_provider_spatialite.py
@@ -39,6 +39,7 @@
     QgsVectorLayerExporter,
     QgsVectorLayerUtils,
     QgsWkbTypes,
+    NULL,
 )
 import unittest
 from qgis.testing import start_app, QgisTestCase
@@ -1552,9 +1553,8 @@ def testSpatialiteDefaultValues(self):
 
         # Test default values
         dp = vl.dataProvider()
-        # FIXME: should it be None?
-        self.assertTrue(dp.defaultValue(0).isNull())
-        self.assertIsNone(dp.defaultValue(1))
+        self.assertEqual(dp.defaultValue(0), NULL)
+        self.assertEqual(dp.defaultValue(1), NULL)
         # FIXME: This fails because there is no backend-side evaluation in this provider
         # self.assertTrue(dp.defaultValue(2).startswith(now.strftime('%Y-%m-%d')))
         self.assertTrue(dp.defaultValue(
diff --git a/tests/src/python/test_python_repr.py b/tests/src/python/test_python_repr.py
index 43cc0a46ebd2..677005b801a3 100644
--- a/tests/src/python/test_python_repr.py
+++ b/tests/src/python/test_python_repr.py
@@ -177,6 +177,8 @@ def testQgsPolygonRepr(self):
     def testQgsRectangleRepr(self):
         r = QgsRectangle(1, 2, 3, 4)
         self.assertEqual(r.__repr__(), '<QgsRectangle: 1 2, 3 4>')
+        r = QgsRectangle()
+        self.assertEqual(r.__repr__(), '<QgsRectangle()>')
 
     def testQgsReferencedRectangleRepr(self):
         r = QgsReferencedRectangle(QgsRectangle(1, 2, 3, 4), QgsCoordinateReferenceSystem('EPSG:4326'))
diff --git a/tests/src/python/test_qgsfeatureiterator.py b/tests/src/python/test_qgsfeatureiterator.py
index 93b58e859cc3..898a06e58614 100644
--- a/tests/src/python/test_qgsfeatureiterator.py
+++ b/tests/src/python/test_qgsfeatureiterator.py
@@ -116,6 +116,29 @@ def addFeatures(self, vl):
         feat['Staff'] = 2
         vl.addFeature(feat)
 
+    def test_VectorLayerEditing(self):
+        ogr_layer = QgsVectorLayer(os.path.join(TEST_DATA_DIR, 'points.shp'), 'Points', 'ogr')
+        self.assertTrue(ogr_layer.isValid())
+
+        request = QgsFeatureRequest()
+        iterator = ogr_layer.getFeatures(request)
+        self.assertTrue(iterator.isValid())
+
+        self.assertTrue(ogr_layer.startEditing())
+        iterator = ogr_layer.getFeatures(request)
+        self.assertTrue(iterator.isValid())
+
+        memory_layer = QgsVectorLayer("Point?field=x:string&field=y:integer&field=z:integer", "layer", "memory")
+        self.assertTrue(memory_layer.isValid())
+
+        request = QgsFeatureRequest()
+        iterator = memory_layer.getFeatures(request)
+        self.assertTrue(iterator.isValid())
+
+        self.assertTrue(memory_layer.startEditing())
+        iterator = memory_layer.getFeatures(request)
+        self.assertTrue(iterator.isValid())
+
     def test_ExpressionFieldNested(self):
         myShpFile = os.path.join(TEST_DATA_DIR, 'points.shp')
         layer = QgsVectorLayer(myShpFile, 'Points', 'ogr')
diff --git a/tests/src/python/test_qgsserver_wms_getmap.py b/tests/src/python/test_qgsserver_wms_getmap.py
index a4a57460af9c..6956bff2cc64 100644
--- a/tests/src/python/test_qgsserver_wms_getmap.py
+++ b/tests/src/python/test_qgsserver_wms_getmap.py
@@ -336,6 +336,25 @@ def test_wms_getmap_invalid_parameters(self):
         err = b"HEIGHT (\'FOO\') cannot be converted into int" in r
         self.assertTrue(err)
 
+        # height should be > 0
+        qs = "?" + "&".join(["%s=%s" % i for i in list({
+            "MAP": urllib.parse.quote(self.projectPath),
+            "SERVICE": "WMS",
+            "VERSION": "1.1.1",
+            "REQUEST": "GetMap",
+            "LAYERS": "Country",
+            "STYLES": "",
+            "FORMAT": "image/png",
+            "BBOX": "-16817707,-4710778,5696513,14587125",
+            "HEIGHT": "-1",
+            "WIDTH": "1",
+            "CRS": "EPSG:3857"
+        }.items())])
+
+        r, h = self._result(self._execute_request(qs))
+        err = b"The requested map size is too large" in r
+        self.assertTrue(err)
+
         # width should be an int
         qs = "?" + "&".join(["%s=%s" % i for i in list({
             "MAP": urllib.parse.quote(self.projectPath),
@@ -355,6 +374,25 @@ def test_wms_getmap_invalid_parameters(self):
         err = b"WIDTH (\'FOO\') cannot be converted into int" in r
         self.assertTrue(err)
 
+        # width should be > 0
+        qs = "?" + "&".join(["%s=%s" % i for i in list({
+            "MAP": urllib.parse.quote(self.projectPath),
+            "SERVICE": "WMS",
+            "VERSION": "1.1.1",
+            "REQUEST": "GetMap",
+            "LAYERS": "Country",
+            "STYLES": "",
+            "FORMAT": "image/png",
+            "BBOX": "-16817707,-4710778,5696513,14587125",
+            "HEIGHT": "1",
+            "WIDTH": "-1",
+            "CRS": "EPSG:3857"
+        }.items())])
+
+        r, h = self._result(self._execute_request(qs))
+        err = b"The requested map size is too large" in r
+        self.assertTrue(err)
+
         # bbox should be formatted like "double,double,double,double"
         qs = "?" + "&".join(["%s=%s" % i for i in list({
             "MAP": urllib.parse.quote(self.projectPath),
diff --git a/tests/testdata/qgis_server/wfs_getFeature_1_1_0_featureid_0_1_1_0_srsname.txt b/tests/testdata/qgis_server/wfs_getFeature_1_1_0_featureid_0_1_1_0_srsname.txt
index ce39f88833d0..c5c1206856e6 100644
--- a/tests/testdata/qgis_server/wfs_getFeature_1_1_0_featureid_0_1_1_0_srsname.txt
+++ b/tests/testdata/qgis_server/wfs_getFeature_1_1_0_featureid_0_1_1_0_srsname.txt
@@ -3,21 +3,21 @@ Content-Type: text/xml; subtype=gml/3.1.1; charset=utf-8
 <wfs:FeatureCollection xmlns:wfs="http://www.opengis.net/wfs" xmlns:ogc="http://www.opengis.net/ogc" xmlns:gml="http://www.opengis.net/gml" xmlns:ows="http://www.opengis.net/ows" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:qgs="http://www.qgis.org/gml" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.opengis.net/wfs http://schemas.opengis.net/wfs/1.1.0/wfs.xsd http://www.qgis.org/gml ?MAP=/home/etienne/dev/qgis/qgis-master/tests/testdata/qgis_server/test_project_wfs.qgs&amp;SERVICE=WFS&amp;VERSION=1.1.0&amp;REQUEST=DescribeFeatureType&amp;TYPENAME=testlayer&amp;OUTPUTFORMAT=text/xml; subtype%3Dgml/3.1.1">
 <gml:boundedBy>
  <gml:Envelope srsName="EPSG:4326">
-  <gml:lowerCorner>44.90139484 8.20345931</gml:lowerCorner>
-  <gml:upperCorner>44.90148253 8.20354699</gml:upperCorner>
+  <gml:lowerCorner>8.20345931 44.90139484</gml:lowerCorner>
+  <gml:upperCorner>8.20354699 44.90148253</gml:upperCorner>
  </gml:Envelope>
 </gml:boundedBy>
 <gml:featureMember>
  <qgs:testlayer gml:id="testlayer.0">
   <gml:boundedBy>
    <gml:Envelope srsName="EPSG:4326">
-    <gml:lowerCorner>44.90148253 8.20349634</gml:lowerCorner>
-    <gml:upperCorner>44.90148253 8.20349634</gml:upperCorner>
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