diff --git a/packages/blockly/core/serialization/blocks.ts b/packages/blockly/core/serialization/blocks.ts
index af8910b3137..7afa363b99b 100644
--- a/packages/blockly/core/serialization/blocks.ts
+++ b/packages/blockly/core/serialization/blocks.ts
@@ -601,18 +601,27 @@ function tryToConnectParent(
 
   if (!connected) {
     const checker = child.workspace.connectionChecker;
-    throw new BadConnectionCheck(
-      checker.getErrorMessage(
-        checker.canConnectWithReason(childConnection, parentConnection, false),
-        childConnection,
-        parentConnection,
-      ),
-      parentConnection.type === inputTypes.VALUE
-        ? 'output connection'
-        : 'previous connection',
-      child,
-      state,
+    const reason = checker.getErrorMessage(
+      checker.canConnectWithReason(childConnection, parentConnection, false),
+      childConnection,
+      parentConnection,
     );
+    if (child.isShadow()) {
+      throw new BadConnectionCheck(
+        reason,
+        parentConnection.type === inputTypes.VALUE
+          ? 'output connection'
+          : 'previous connection',
+        child,
+        state,
+      );
+    }
+    console.warn(
+      `Connection check failed during JSON deserialization: ${reason}. ` +
+        `Block "${child.type}" (${child.id}) will be placed as a ` +
+        `top-level block instead.`,
+    );
+    child.setDisabledReason(true, 'orphaned_connection_check');
   }
 }
 
diff --git a/packages/blockly/core/xml.ts b/packages/blockly/core/xml.ts
index 3c06a39cca9..05654e6ee04 100644
--- a/packages/blockly/core/xml.ts
+++ b/packages/blockly/core/xml.ts
@@ -636,6 +636,7 @@ export function domToBlockInternal(
   // Create top-level block.
   eventUtils.disable();
   const variablesBeforeCreation = workspace.getVariableMap().getAllVariables();
+  const topBlocksBefore = new Set(workspace.getTopBlocks(false));
   let topBlock;
   try {
     topBlock = domToBlockHeadless(xmlBlock, workspace);
@@ -651,6 +652,30 @@ export function domToBlockInternal(
       for (let i = blocks.length - 1; i >= 0; i--) {
         (blocks[i] as BlockSvg).queueRender();
       }
+
+      // Initialize any orphaned blocks that failed to connect during
+      // deserialization (e.g. due to connection type check failures).
+      // These blocks were created but are not descendants of topBlock.
+      const connectedBlocks = new Set(blocks);
+      for (const block of workspace.getTopBlocks(false)) {
+        if (topBlocksBefore.has(block) || connectedBlocks.has(block)) continue;
+        const orphanSvg = block as BlockSvg;
+        orphanSvg.setConnectionTracking(false);
+        block.setDisabledReason(true, 'orphaned_connection_check');
+        const orphanDescendants = block.getDescendants(false);
+        for (let i = orphanDescendants.length - 1; i >= 0; i--) {
+          (orphanDescendants[i] as BlockSvg).initSvg();
+        }
+        for (let i = orphanDescendants.length - 1; i >= 0; i--) {
+          (orphanDescendants[i] as BlockSvg).queueRender();
+        }
+        setTimeout(function () {
+          if (!orphanSvg.disposed) {
+            orphanSvg.setConnectionTracking(true);
+          }
+        }, 1);
+      }
+
       // Populating the connection database may be deferred until after the
       // blocks have rendered.
       setTimeout(function () {
@@ -666,6 +691,16 @@ export function domToBlockInternal(
       for (let i = blocks.length - 1; i >= 0; i--) {
         blocks[i].initModel();
       }
+      // Initialize orphaned blocks on headless workspaces too.
+      const connectedBlocks = new Set(blocks);
+      for (const block of workspace.getTopBlocks(false)) {
+        if (topBlocksBefore.has(block) || connectedBlocks.has(block)) continue;
+        block.setDisabledReason(true, 'orphaned_connection_check');
+        const orphanDescendants = block.getDescendants(false);
+        for (let i = orphanDescendants.length - 1; i >= 0; i--) {
+          orphanDescendants[i].initModel();
+        }
+      }
     }
   } finally {
     eventUtils.enable();
diff --git a/packages/blockly/tests/mocha/jso_deserialization_test.js b/packages/blockly/tests/mocha/jso_deserialization_test.js
index f6b47d7de6a..c4ad624b90d 100644
--- a/packages/blockly/tests/mocha/jso_deserialization_test.js
+++ b/packages/blockly/tests/mocha/jso_deserialization_test.js
@@ -14,6 +14,7 @@ import {
 import {
   sharedTestSetup,
   sharedTestTeardown,
+  workspaceTeardown,
 } from './test_helpers/setup_teardown.js';
 
 suite('JSO Deserialization', function () {
@@ -630,10 +631,50 @@ suite('JSO Deserialization', function () {
             ],
           },
         };
-        this.assertThrows(
-          state,
-          Blockly.serialization.exceptions.BadConnectionCheck,
-        );
+        Blockly.serialization.workspaces.load(state, this.workspace);
+
+        const allBlocks = this.workspace.getAllBlocks(false);
+        assert.equal(allBlocks.length, 2, 'Both blocks exist');
+
+        const mathBlock = allBlocks.find((b) => b.type === 'math_number');
+        assert.isNotNull(mathBlock, 'math_number block exists');
+        assert.isNull(mathBlock.getParent(), 'Orphan has no parent');
+      });
+
+      test('Bad checks - orphan SVG is initialized on rendered workspace', function () {
+        const workspace = Blockly.inject('blocklyDiv');
+        try {
+          const state = {
+            'blocks': {
+              'blocks': [
+                {
+                  'type': 'logic_operation',
+                  'inputs': {
+                    'A': {
+                      'block': {
+                        'type': 'math_number',
+                      },
+                    },
+                  },
+                },
+              ],
+            },
+          };
+          Blockly.serialization.workspaces.load(state, workspace);
+          this.clock.runAll();
+
+          const allBlocks = workspace.getAllBlocks(false);
+          assert.equal(allBlocks.length, 2, 'Both blocks exist');
+
+          const mathBlock = allBlocks.find((b) => b.type === 'math_number');
+          assert.isNotNull(mathBlock, 'math_number block exists');
+          assert.isNotNull(
+            mathBlock.getSvgRoot().parentNode,
+            'Orphan SVG is in the DOM',
+          );
+        } finally {
+          workspaceTeardown.call(this, workspace);
+        }
       });
     });
 
diff --git a/packages/blockly/tests/mocha/xml_test.js b/packages/blockly/tests/mocha/xml_test.js
index 94219f9a067..f1106c572a9 100644
--- a/packages/blockly/tests/mocha/xml_test.js
+++ b/packages/blockly/tests/mocha/xml_test.js
@@ -890,4 +890,90 @@ suite('XML', function () {
       });
     });
   });
+
+  suite('Connection check failures', function () {
+    setup(function () {
+      Blockly.defineBlocksWithJsonArray([
+        {
+          'type': 'typed_input_block',
+          'message0': '%1',
+          'args0': [
+            {
+              'type': 'input_value',
+              'name': 'INPUT',
+              'check': 'Int',
+            },
+          ],
+        },
+        {
+          'type': 'typed_output_block',
+          'message0': '',
+          'output': 'Long',
+        },
+      ]);
+      addBlockTypeToCleanup(this.sharedCleanup, 'typed_input_block');
+      addBlockTypeToCleanup(this.sharedCleanup, 'typed_output_block');
+    });
+
+    test('Orphaned block SVG is in the DOM on rendered workspace', function () {
+      this.workspace = Blockly.inject('blocklyDiv');
+      const xml = Blockly.utils.xml.textToDom(
+        '<xml>' +
+          '<block type="typed_input_block" x="10" y="10">' +
+          '  <value name="INPUT">' +
+          '    <block type="typed_output_block"/>' +
+          '  </value>' +
+          '</block>' +
+          '</xml>',
+      );
+      Blockly.Xml.domToWorkspace(xml, this.workspace);
+      this.clock.runAll();
+
+      const allBlocks = this.workspace.getAllBlocks(false);
+      assert.equal(allBlocks.length, 2, 'Both blocks exist');
+
+      const topBlocks = this.workspace.getTopBlocks(false);
+      assert.equal(topBlocks.length, 2, 'Both blocks are top-level');
+
+      const outputBlock = allBlocks.find(
+        (b) => b.type === 'typed_output_block',
+      );
+      assert.isNotNull(
+        outputBlock.getSvgRoot().parentNode,
+        'Orphaned block SVG is in the DOM',
+      );
+      assert.isNull(outputBlock.getParent(), 'Orphaned block has no parent');
+
+      workspaceTeardown.call(this, this.workspace);
+    });
+
+    test('Orphaned block is initialized on headless workspace', function () {
+      const workspace = new Blockly.Workspace();
+      try {
+        const xml = Blockly.utils.xml.textToDom(
+          '<xml>' +
+            '<block type="typed_input_block" x="10" y="10">' +
+            '  <value name="INPUT">' +
+            '    <block type="typed_output_block"/>' +
+            '  </value>' +
+            '</block>' +
+            '</xml>',
+        );
+        Blockly.Xml.domToWorkspace(xml, workspace);
+
+        const allBlocks = workspace.getAllBlocks(false);
+        assert.equal(allBlocks.length, 2, 'Both blocks exist');
+
+        const topBlocks = workspace.getTopBlocks(false);
+        assert.equal(topBlocks.length, 2, 'Both blocks are top-level');
+
+        const outputBlock = allBlocks.find(
+          (b) => b.type === 'typed_output_block',
+        );
+        assert.isNull(outputBlock.getParent(), 'Orphaned block has no parent');
+      } finally {
+        workspaceTeardown.call(this, workspace);
+      }
+    });
+  });
 });