diff --git a/CHANGES.md b/CHANGES.md
index 29711c60ce6c..5d4e80499eec 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -1,3 +1,20 @@
+Synapse 1.21.0rc2 (2020-10-02)
+==============================
+
+Features
+--------
+
+- Convert additional templates from inline HTML to Jinja2 templates. ([\#8444](https://github.com/matrix-org/synapse/issues/8444))
+
+Bugfixes
+--------
+
+- Fix a regression in v1.21.0rc1 which broke thumbnails of remote media. ([\#8438](https://github.com/matrix-org/synapse/issues/8438))
+- Do not expose the experimental `uk.half-shot.msc2778.login.application_service` flow in the login API, which caused a compatibility problem with Element iOS. ([\#8440](https://github.com/matrix-org/synapse/issues/8440))
+- Fix malformed log line in new federation "catch up" logic. ([\#8442](https://github.com/matrix-org/synapse/issues/8442))
+- Fix DB query on startup for negative streams which caused long start up times. Introduced in [\#8374](https://github.com/matrix-org/synapse/issues/8374). ([\#8447](https://github.com/matrix-org/synapse/issues/8447))
+
+
 Synapse 1.21.0rc1 (2020-10-01)
 ==============================
 
diff --git a/synapse/__init__.py b/synapse/__init__.py
index 47069745080f..500558bbdf8b 100644
--- a/synapse/__init__.py
+++ b/synapse/__init__.py
@@ -48,7 +48,7 @@
 except ImportError:
     pass
 
-__version__ = "1.21.0rc1"
+__version__ = "1.21.0rc2"
 
 if bool(os.environ.get("SYNAPSE_TEST_PATCH_LOG_CONTEXTS", False)):
     # We import here so that we don't have to install a bunch of deps when
diff --git a/synapse/config/_base.py b/synapse/config/_base.py
index 05a66841c338..85f65da4d95f 100644
--- a/synapse/config/_base.py
+++ b/synapse/config/_base.py
@@ -242,12 +242,11 @@ def read_templates(
         env = jinja2.Environment(loader=loader, autoescape=autoescape)
 
         # Update the environment with our custom filters
-        env.filters.update(
-            {
-                "format_ts": _format_ts_filter,
-                "mxc_to_http": _create_mxc_to_http_filter(self.public_baseurl),
-            }
-        )
+        env.filters.update({"format_ts": _format_ts_filter})
+        if self.public_baseurl:
+            env.filters.update(
+                {"mxc_to_http": _create_mxc_to_http_filter(self.public_baseurl)}
+            )
 
         for filename in filenames:
             # Load the template
diff --git a/synapse/config/captcha.py b/synapse/config/captcha.py
index 82f04d7966e2..cb009581651b 100644
--- a/synapse/config/captcha.py
+++ b/synapse/config/captcha.py
@@ -28,6 +28,9 @@ def read_config(self, config, **kwargs):
             "recaptcha_siteverify_api",
             "https://www.recaptcha.net/recaptcha/api/siteverify",
         )
+        self.recaptcha_template = self.read_templates(
+            ["recaptcha.html"], autoescape=True
+        )[0]
 
     def generate_config_section(self, **kwargs):
         return """\
diff --git a/synapse/config/consent_config.py b/synapse/config/consent_config.py
index fbddebeeab2a..6efa59b110b0 100644
--- a/synapse/config/consent_config.py
+++ b/synapse/config/consent_config.py
@@ -89,6 +89,8 @@ def __init__(self, *args):
 
     def read_config(self, config, **kwargs):
         consent_config = config.get("user_consent")
+        self.terms_template = self.read_templates(["terms.html"], autoescape=True)[0]
+
         if consent_config is None:
             return
         self.user_consent_version = str(consent_config["version"])
diff --git a/synapse/config/registration.py b/synapse/config/registration.py
index 5ffbb934fe2d..d7e3690a32fb 100644
--- a/synapse/config/registration.py
+++ b/synapse/config/registration.py
@@ -187,6 +187,11 @@ def read_config(self, config, **kwargs):
             session_lifetime = self.parse_duration(session_lifetime)
         self.session_lifetime = session_lifetime
 
+        # The success template used during fallback auth.
+        self.fallback_success_template = self.read_templates(
+            ["auth_success.html"], autoescape=True
+        )[0]
+
     def generate_config_section(self, generate_secrets=False, **kwargs):
         if generate_secrets:
             registration_shared_secret = 'registration_shared_secret: "%s"' % (
diff --git a/synapse/federation/sender/per_destination_queue.py b/synapse/federation/sender/per_destination_queue.py
index 2657767fd153..bc99af3fdd80 100644
--- a/synapse/federation/sender/per_destination_queue.py
+++ b/synapse/federation/sender/per_destination_queue.py
@@ -490,7 +490,7 @@ async def _catch_up_transmission_loop(self) -> None:
                 )
 
             if logger.isEnabledFor(logging.INFO):
-                rooms = (p.room_id for p in catchup_pdus)
+                rooms = [p.room_id for p in catchup_pdus]
                 logger.info("Catching up rooms to %s: %r", self._destination, rooms)
 
             success = await self._transaction_manager.send_new_transaction(
diff --git a/synapse/res/templates/auth_success.html b/synapse/res/templates/auth_success.html
new file mode 100644
index 000000000000..baf463314258
--- /dev/null
+++ b/synapse/res/templates/auth_success.html
@@ -0,0 +1,21 @@
+<html>
+<head>
+<title>Success!</title>
+<meta name='viewport' content='width=device-width, initial-scale=1,
+    user-scalable=no, minimum-scale=1.0, maximum-scale=1.0'>
+<link rel="stylesheet" href="/_matrix/static/client/register/style.css">
+<script>
+if (window.onAuthDone) {
+    window.onAuthDone();
+} else if (window.opener && window.opener.postMessage) {
+     window.opener.postMessage("authDone", "*");
+}
+</script>
+</head>
+<body>
+    <div>
+        <p>Thank you</p>
+        <p>You may now close this window and return to the application</p>
+    </div>
+</body>
+</html>
diff --git a/synapse/res/templates/recaptcha.html b/synapse/res/templates/recaptcha.html
new file mode 100644
index 000000000000..63944dc60814
--- /dev/null
+++ b/synapse/res/templates/recaptcha.html
@@ -0,0 +1,38 @@
+<html>
+<head>
+<title>Authentication</title>
+<meta name='viewport' content='width=device-width, initial-scale=1,
+    user-scalable=no, minimum-scale=1.0, maximum-scale=1.0'>
+<script src="https://www.recaptcha.net/recaptcha/api.js"
+    async defer></script>
+<script src="//code.jquery.com/jquery-1.11.2.min.js"></script>
+<link rel="stylesheet" href="/_matrix/static/client/register/style.css">
+<script>
+function captchaDone() {
+    $('#registrationForm').submit();
+}
+</script>
+</head>
+<body>
+<form id="registrationForm" method="post" action="{{ myurl }}">
+    <div>
+        <p>
+        Hello! We need to prevent computer programs and other automated
+        things from creating accounts on this server.
+        </p>
+        <p>
+        Please verify that you're not a robot.
+        </p>
+        <input type="hidden" name="session" value="{{ session }}" />
+        <div class="g-recaptcha"
+            data-sitekey="{{ sitekey }}"
+            data-callback="captchaDone">
+        </div>
+        <noscript>
+        <input type="submit" value="All Done" />
+        </noscript>
+        </div>
+    </div>
+</form>
+</body>
+</html>
diff --git a/synapse/res/templates/terms.html b/synapse/res/templates/terms.html
new file mode 100644
index 000000000000..dfef9897ee40
--- /dev/null
+++ b/synapse/res/templates/terms.html
@@ -0,0 +1,20 @@
+<html>
+<head>
+<title>Authentication</title>
+<meta name='viewport' content='width=device-width, initial-scale=1,
+    user-scalable=no, minimum-scale=1.0, maximum-scale=1.0'>
+<link rel="stylesheet" href="/_matrix/static/client/register/style.css">
+</head>
+<body>
+<form id="registrationForm" method="post" action="{{ myurl }}">
+    <div>
+        <p>
+            Please click the button below if you agree to the
+            <a href="{{ terms_url }}">privacy policy of this homeserver.</a>
+        </p>
+        <input type="hidden" name="session" value="{{ session }}" />
+        <input type="submit" value="Agree" />
+    </div>
+</form>
+</body>
+</html>
diff --git a/synapse/rest/client/v1/login.py b/synapse/rest/client/v1/login.py
index b9347b87c7c6..3d1693d7acfb 100644
--- a/synapse/rest/client/v1/login.py
+++ b/synapse/rest/client/v1/login.py
@@ -111,8 +111,6 @@ def on_GET(self, request: SynapseRequest):
             ({"type": t} for t in self.auth_handler.get_supported_login_types())
         )
 
-        flows.append({"type": LoginRestServlet.APPSERVICE_TYPE})
-
         return 200, {"flows": flows}
 
     def on_OPTIONS(self, request: SynapseRequest):
diff --git a/synapse/rest/client/v2_alpha/auth.py b/synapse/rest/client/v2_alpha/auth.py
index 097538f96864..5fbfae599101 100644
--- a/synapse/rest/client/v2_alpha/auth.py
+++ b/synapse/rest/client/v2_alpha/auth.py
@@ -25,94 +25,6 @@
 
 logger = logging.getLogger(__name__)
 
-RECAPTCHA_TEMPLATE = """
-<html>
-<head>
-<title>Authentication</title>
-<meta name='viewport' content='width=device-width, initial-scale=1,
-    user-scalable=no, minimum-scale=1.0, maximum-scale=1.0'>
-<script src="https://www.recaptcha.net/recaptcha/api.js"
-    async defer></script>
-<script src="//code.jquery.com/jquery-1.11.2.min.js"></script>
-<link rel="stylesheet" href="/_matrix/static/client/register/style.css">
-<script>
-function captchaDone() {
-    $('#registrationForm').submit();
-}
-</script>
-</head>
-<body>
-<form id="registrationForm" method="post" action="%(myurl)s">
-    <div>
-        <p>
-        Hello! We need to prevent computer programs and other automated
-        things from creating accounts on this server.
-        </p>
-        <p>
-        Please verify that you're not a robot.
-        </p>
-        <input type="hidden" name="session" value="%(session)s" />
-        <div class="g-recaptcha"
-            data-sitekey="%(sitekey)s"
-            data-callback="captchaDone">
-        </div>
-        <noscript>
-        <input type="submit" value="All Done" />
-        </noscript>
-        </div>
-    </div>
-</form>
-</body>
-</html>
-"""
-
-TERMS_TEMPLATE = """
-<html>
-<head>
-<title>Authentication</title>
-<meta name='viewport' content='width=device-width, initial-scale=1,
-    user-scalable=no, minimum-scale=1.0, maximum-scale=1.0'>
-<link rel="stylesheet" href="/_matrix/static/client/register/style.css">
-</head>
-<body>
-<form id="registrationForm" method="post" action="%(myurl)s">
-    <div>
-        <p>
-            Please click the button below if you agree to the
-            <a href="%(terms_url)s">privacy policy of this homeserver.</a>
-        </p>
-        <input type="hidden" name="session" value="%(session)s" />
-        <input type="submit" value="Agree" />
-    </div>
-</form>
-</body>
-</html>
-"""
-
-SUCCESS_TEMPLATE = """
-<html>
-<head>
-<title>Success!</title>
-<meta name='viewport' content='width=device-width, initial-scale=1,
-    user-scalable=no, minimum-scale=1.0, maximum-scale=1.0'>
-<link rel="stylesheet" href="/_matrix/static/client/register/style.css">
-<script>
-if (window.onAuthDone) {
-    window.onAuthDone();
-} else if (window.opener && window.opener.postMessage) {
-     window.opener.postMessage("authDone", "*");
-}
-</script>
-</head>
-<body>
-    <div>
-        <p>Thank you</p>
-        <p>You may now close this window and return to the application</p>
-    </div>
-</body>
-</html>
-"""
-
 
 class AuthRestServlet(RestServlet):
     """
@@ -145,26 +57,30 @@ def __init__(self, hs):
             self._cas_server_url = hs.config.cas_server_url
             self._cas_service_url = hs.config.cas_service_url
 
+        self.recaptcha_template = hs.config.recaptcha_template
+        self.terms_template = hs.config.terms_template
+        self.success_template = hs.config.fallback_success_template
+
     async def on_GET(self, request, stagetype):
         session = parse_string(request, "session")
         if not session:
             raise SynapseError(400, "No session supplied")
 
         if stagetype == LoginType.RECAPTCHA:
-            html = RECAPTCHA_TEMPLATE % {
-                "session": session,
-                "myurl": "%s/r0/auth/%s/fallback/web"
+            html = self.recaptcha_template.render(
+                session=session,
+                myurl="%s/r0/auth/%s/fallback/web"
                 % (CLIENT_API_PREFIX, LoginType.RECAPTCHA),
-                "sitekey": self.hs.config.recaptcha_public_key,
-            }
+                sitekey=self.hs.config.recaptcha_public_key,
+            )
         elif stagetype == LoginType.TERMS:
-            html = TERMS_TEMPLATE % {
-                "session": session,
-                "terms_url": "%s_matrix/consent?v=%s"
+            html = self.terms_template.render(
+                session=session,
+                terms_url="%s_matrix/consent?v=%s"
                 % (self.hs.config.public_baseurl, self.hs.config.user_consent_version),
-                "myurl": "%s/r0/auth/%s/fallback/web"
+                myurl="%s/r0/auth/%s/fallback/web"
                 % (CLIENT_API_PREFIX, LoginType.TERMS),
-            }
+            )
 
         elif stagetype == LoginType.SSO:
             # Display a confirmation page which prompts the user to
@@ -222,14 +138,14 @@ async def on_POST(self, request, stagetype):
             )
 
             if success:
-                html = SUCCESS_TEMPLATE
+                html = self.success_template.render()
             else:
-                html = RECAPTCHA_TEMPLATE % {
-                    "session": session,
-                    "myurl": "%s/r0/auth/%s/fallback/web"
+                html = self.recaptcha_template.render(
+                    session=session,
+                    myurl="%s/r0/auth/%s/fallback/web"
                     % (CLIENT_API_PREFIX, LoginType.RECAPTCHA),
-                    "sitekey": self.hs.config.recaptcha_public_key,
-                }
+                    sitekey=self.hs.config.recaptcha_public_key,
+                )
         elif stagetype == LoginType.TERMS:
             authdict = {"session": session}
 
@@ -238,18 +154,18 @@ async def on_POST(self, request, stagetype):
             )
 
             if success:
-                html = SUCCESS_TEMPLATE
+                html = self.success_template.render()
             else:
-                html = TERMS_TEMPLATE % {
-                    "session": session,
-                    "terms_url": "%s_matrix/consent?v=%s"
+                html = self.terms_template.render(
+                    session=session,
+                    terms_url="%s_matrix/consent?v=%s"
                     % (
                         self.hs.config.public_baseurl,
                         self.hs.config.user_consent_version,
                     ),
-                    "myurl": "%s/r0/auth/%s/fallback/web"
+                    myurl="%s/r0/auth/%s/fallback/web"
                     % (CLIENT_API_PREFIX, LoginType.TERMS),
-                }
+                )
         elif stagetype == LoginType.SSO:
             # The SSO fallback workflow should not post here,
             raise SynapseError(404, "Fallback SSO auth does not support POST requests.")
diff --git a/synapse/rest/media/v1/media_storage.py b/synapse/rest/media/v1/media_storage.py
index 5681677fc93d..a9586fb0b73d 100644
--- a/synapse/rest/media/v1/media_storage.py
+++ b/synapse/rest/media/v1/media_storage.py
@@ -141,31 +141,34 @@ async def fetch_media(self, file_info: FileInfo) -> Optional[Responder]:
         Returns:
             Returns a Responder if the file was found, otherwise None.
         """
+        paths = [self._file_info_to_path(file_info)]
 
-        path = self._file_info_to_path(file_info)
-        local_path = os.path.join(self.local_media_directory, path)
-        if os.path.exists(local_path):
-            return FileResponder(open(local_path, "rb"))
-
-        # Fallback for paths without method names
-        # Should be removed in the future
+        # fallback for remote thumbnails with no method in the filename
         if file_info.thumbnail and file_info.server_name:
-            legacy_path = self.filepaths.remote_media_thumbnail_rel_legacy(
-                server_name=file_info.server_name,
-                file_id=file_info.file_id,
-                width=file_info.thumbnail_width,
-                height=file_info.thumbnail_height,
-                content_type=file_info.thumbnail_type,
+            paths.append(
+                self.filepaths.remote_media_thumbnail_rel_legacy(
+                    server_name=file_info.server_name,
+                    file_id=file_info.file_id,
+                    width=file_info.thumbnail_width,
+                    height=file_info.thumbnail_height,
+                    content_type=file_info.thumbnail_type,
+                )
             )
-            legacy_local_path = os.path.join(self.local_media_directory, legacy_path)
-            if os.path.exists(legacy_local_path):
-                return FileResponder(open(legacy_local_path, "rb"))
+
+        for path in paths:
+            local_path = os.path.join(self.local_media_directory, path)
+            if os.path.exists(local_path):
+                logger.debug("responding with local file %s", local_path)
+                return FileResponder(open(local_path, "rb"))
+            logger.debug("local file %s did not exist", local_path)
 
         for provider in self.storage_providers:
-            res = await provider.fetch(path, file_info)  # type: Any
-            if res:
-                logger.debug("Streaming %s from %s", path, provider)
-                return res
+            for path in paths:
+                res = await provider.fetch(path, file_info)  # type: Any
+                if res:
+                    logger.debug("Streaming %s from %s", path, provider)
+                    return res
+                logger.debug("%s not found on %s", path, provider)
 
         return None
 
diff --git a/synapse/storage/util/id_generators.py b/synapse/storage/util/id_generators.py
index ec356b2e4f06..c92cd4a6bae3 100644
--- a/synapse/storage/util/id_generators.py
+++ b/synapse/storage/util/id_generators.py
@@ -341,7 +341,7 @@ def _load_current_ids(
                 "cmp": "<=" if self._positive else ">=",
             }
             sql = self._db.engine.convert_param_style(sql)
-            cur.execute(sql, (min_stream_id,))
+            cur.execute(sql, (min_stream_id * self._return_factor,))
 
             self._persisted_upto_position = min_stream_id