diff --git a/packages/block-editor/src/components/block-list/block-html.js b/packages/block-editor/src/components/block-list/block-html.js
index 5d9e7bfeb7bf77..c670133de17c41 100644
--- a/packages/block-editor/src/components/block-list/block-html.js
+++ b/packages/block-editor/src/components/block-list/block-html.js
@@ -6,7 +6,7 @@ import TextareaAutosize from 'react-autosize-textarea';
 /**
  * WordPress dependencies
  */
-import { useEffect, useState } from '@wordpress/element';
+import { useEffect, useMemo, useState } from '@wordpress/element';
 import { useSelect, useDispatch } from '@wordpress/data';
 import {
 	getBlockAttributes,
@@ -28,6 +28,16 @@ function BlockHTML( { clientId } ) {
 		[ clientId ]
 	);
 	const { updateBlock } = useDispatch( blockEditorStore );
+
+	// Derive block content as a primitive string so the effect only fires
+	// when the serialized content genuinely changes, not when the block
+	// object reference changes (which happens on every RESET_BLOCKS during
+	// RTC sync, even for unchanged blocks).
+	const blockContent = useMemo(
+		() => ( block ? getBlockContent( block ) : '' ),
+		[ block ]
+	);
+
 	const onChange = () => {
 		const blockType = getBlockType( block.name );
 
@@ -64,8 +74,8 @@ function BlockHTML( { clientId } ) {
 	};
 
 	useEffect( () => {
-		setHtml( getBlockContent( block ) );
-	}, [ block ] );
+		setHtml( blockContent );
+	}, [ blockContent ] );
 
 	return (
 		<TextareaAutosize