diff --git a/assets/js/atomic/utils/register-block-single-product-template.ts b/assets/js/atomic/utils/register-block-single-product-template.ts
index d1e853acbe9..5d7e1ab020f 100644
--- a/assets/js/atomic/utils/register-block-single-product-template.ts
+++ b/assets/js/atomic/utils/register-block-single-product-template.ts
@@ -1,6 +1,7 @@
 /**
  * External dependencies
  */
+import { isNumber } from '@woocommerce/types';
 import {
 	BlockAttributes,
 	BlockConfiguration,
@@ -16,8 +17,10 @@ import { subscribe, select } from '@wordpress/data';
 // Creating a local cache to prevent multiple registration tries.
 const blocksRegistered = new Set();
 
-function parseTemplateId( templateId: string | undefined ) {
-	return templateId?.split( '//' )[ 1 ];
+function parseTemplateId( templateId: string | number | undefined ) {
+	// With GB 16.3.0 the return type can be a number: https://github.com/WordPress/gutenberg/issues/53230
+	const parsedTemplateId = isNumber( templateId ) ? undefined : templateId;
+	return parsedTemplateId?.split( '//' )[ 1 ];
 }
 
 export const registerBlockSingleProductTemplate = ( {
@@ -40,7 +43,11 @@ export const registerBlockSingleProductTemplate = ( {
 	subscribe( () => {
 		const previousTemplateId = currentTemplateId;
 		const store = select( 'core/edit-site' );
-		currentTemplateId = parseTemplateId( store?.getEditedPostId() );
+
+		// With GB 16.3.0 the return type can be a number: https://github.com/WordPress/gutenberg/issues/53230
+		currentTemplateId = parseTemplateId(
+			store?.getEditedPostId() as string | number | undefined
+		);
 		const hasChangedTemplate = previousTemplateId !== currentTemplateId;
 		const hasTemplateId = Boolean( currentTemplateId );
 
diff --git a/assets/js/blocks/classic-template/index.tsx b/assets/js/blocks/classic-template/index.tsx
index 9d69c00c2b3..7f89427e0a0 100644
--- a/assets/js/blocks/classic-template/index.tsx
+++ b/assets/js/blocks/classic-template/index.tsx
@@ -31,6 +31,7 @@ import { store as noticesStore } from '@wordpress/notices';
 import { useEntityRecord } from '@wordpress/core-data';
 import { debounce } from '@woocommerce/base-utils';
 import { woo } from '@woocommerce/icons';
+import { isNumber } from '@woocommerce/types';
 
 /**
  * Internal dependencies
@@ -417,7 +418,14 @@ let currentTemplateId: string | undefined;
 subscribe( () => {
 	const previousTemplateId = currentTemplateId;
 	const store = select( 'core/edit-site' );
-	currentTemplateId = store?.getEditedPostId() as string | undefined;
+	// With GB 16.3.0 the return type can be a number: https://github.com/WordPress/gutenberg/issues/53230
+	const editedPostId = store?.getEditedPostId() as
+		| string
+		| number
+		| undefined;
+
+	currentTemplateId = isNumber( editedPostId ) ? undefined : editedPostId;
+
 	const parsedTemplate = currentTemplateId?.split( '//' )[ 1 ];
 
 	if ( parsedTemplate === null || parsedTemplate === undefined ) {
diff --git a/composer.json b/composer.json
index 9dd27664ebb..6bd56abb82f 100644
--- a/composer.json
+++ b/composer.json
@@ -3,7 +3,7 @@
 	"description": "WooCommerce blocks for the Gutenberg editor.",
 	"homepage": "https://woocommerce.com/",
 	"type": "wordpress-plugin",
-	"version": "10.6.3",
+	"version": "10.6.4",
 	"keywords": [
 		"gutenberg",
 		"woocommerce",
diff --git a/docs/internal-developers/testing/releases/1064.md b/docs/internal-developers/testing/releases/1064.md
new file mode 100644
index 00000000000..eb126a39c54
--- /dev/null
+++ b/docs/internal-developers/testing/releases/1064.md
@@ -0,0 +1,23 @@
+# Testing notes and ZIP for release 10.6.4
+
+Zip file for testing: [woocommerce-gutenberg-products-block.zip](https://github.com/woocommerce/woocommerce-blocks/files/12262069/woocommerce-gutenberg-products-block.zip)
+
+## WooCommerce Core
+
+### Classic Template block registration: add defensive type handling [#10475](https://github.com/woocommerce/woocommerce-blocks/pull/10475)
+
+1. Ensure that you have installed Gutenberg 16.3.0.
+2. Open the Site Editor.
+3. Click on the navigation.
+4. Click on the pencil (to edit button).
+5. Ensure that the Site Editor doesn't crash
+
+| Before | After |
+|--------|--------|
+| <video src=https://github.com/woocommerce/woocommerce-blocks/assets/4463174/86ce276e-e372-40e1-8142-cfde84e32bd6 /> | <video src=https://github.com/woocommerce/woocommerce-blocks/assets/4463174/e655eab3-6339-47c9-8447-d9b06c55b795/>  |
+
+### Update check for active cart template and migration routine [#10462](https://github.com/woocommerce/woocommerce-blocks/pull/10462)
+
+1. Go to Pages > Cart and edit the page. It will load the site editor. Add some text below the header, for example. Feel free to add anything for testing purposes. Save the template.
+2. Add an item to your cart and then load the Cart page on the front end. Ensure your changes from step 1 are visible.
+3. Go to the WP Dasboard, then WooCommerce > Settings > Advanced and change the cart page slug to something different. Repeat step 2 and ensure it still works with your change visible. Ensure the path to the Cart page shown in your browser is the one you updated it to.
diff --git a/docs/internal-developers/testing/releases/README.md b/docs/internal-developers/testing/releases/README.md
index 8452b043ee2..c47cc9f9d2f 100644
--- a/docs/internal-developers/testing/releases/README.md
+++ b/docs/internal-developers/testing/releases/README.md
@@ -161,6 +161,7 @@ Every release includes specific testing instructions for new features and bug fi
     -   [10.6.1](./1061.md)
     -   [10.6.2](./1062.md)
     -   [10.6.3](./1063.md)
+    -   [10.6.4](./1064.md)
 
 
 
diff --git a/package-lock.json b/package-lock.json
index 13e56b52932..7ea83fc2d3d 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,12 +1,12 @@
 {
 	"name": "@woocommerce/block-library",
-	"version": "10.6.3",
+	"version": "10.6.4",
 	"lockfileVersion": 2,
 	"requires": true,
 	"packages": {
 		"": {
 			"name": "@woocommerce/block-library",
-			"version": "10.6.3",
+			"version": "10.6.4",
 			"hasInstallScript": true,
 			"license": "GPL-3.0+",
 			"dependencies": {
diff --git a/package.json b/package.json
index 0072f572d39..f9c37e77692 100644
--- a/package.json
+++ b/package.json
@@ -2,7 +2,7 @@
 	"name": "@woocommerce/block-library",
 	"title": "WooCommerce Blocks",
 	"author": "Automattic",
-	"version": "10.6.3",
+	"version": "10.6.4",
 	"description": "WooCommerce blocks for the Gutenberg editor.",
 	"homepage": "https://github.com/woocommerce/woocommerce-gutenberg-products-block/",
 	"keywords": [
diff --git a/readme.txt b/readme.txt
index e05f17b5c87..0d5019e0682 100644
--- a/readme.txt
+++ b/readme.txt
@@ -4,7 +4,7 @@ Tags: gutenberg, woocommerce, woo commerce, products, blocks, woocommerce blocks
 Requires at least: 6.2
 Tested up to: 6.2
 Requires PHP: 7.3
-Stable tag: 10.6.3
+Stable tag: 10.6.4
 License: GPLv3
 License URI: https://www.gnu.org/licenses/gpl-3.0.html
 
@@ -81,7 +81,14 @@ Release and roadmap notes available on the [WooCommerce Developers Blog](https:/
 
 == Changelog ==
 
-= 10.6.3 - 2021-08-2 =
+= 10.6.4 - 2021-08-04 =
+
+#### Bug Fixes
+
+- Classic Template block registration: add defensive type handling. ([10475](https://github.com/woocommerce/woocommerce-blocks/pull/10475))
+- Fixed an issue where modifications to the Cart/Checkout templates made in the site editor would not be visible on the front end. [#10462](https://github.com/woocommerce/woocommerce-blocks/pull/10462)
+
+= 10.6.3 - 2021-08-02 =
 
 #### Bug Fixes
 
diff --git a/src/BlockTemplatesController.php b/src/BlockTemplatesController.php
index 76e1d909508..cf7ac242cc0 100644
--- a/src/BlockTemplatesController.php
+++ b/src/BlockTemplatesController.php
@@ -798,7 +798,7 @@ protected function migrate_page( $page_id, $page ) {
 		// Use the page template if it exists, which we'll use over our default template if found.
 		$existing_page_template = BlockTemplateUtils::get_block_template( get_stylesheet() . '//page', 'wp_template' );
 
-		if ( $existing_page_template && ! empty( $existing_page_template->content ) ) {
+		if ( $existing_page_template && ! empty( $existing_page_template->content ) && strstr( $existing_page_template->content, 'wp:post-content' ) ) {
 			// Massage the original content into something we can use. Replace post content with a group block.
 			$pattern          = '/(<!--\s*)wp:post-content(.*?)(\/-->)/';
 			$replacement      = '
@@ -811,15 +811,33 @@ protected function migrate_page( $page_id, $page ) {
 			$template_content = $this->get_default_migrate_page_template( $page );
 		}
 
-		$request = new \WP_REST_Request( 'POST', '/wp/v2/templates/woocommerce/woocommerce//' . $page_id );
-		$request->set_body_params(
+		$new_page_template = BlockTemplateUtils::get_block_template( 'woocommerce/woocommerce//' . $page_id, 'wp_template' );
+
+		// Check template validity--template must exist, and custom template must not be present already.
+		if ( ! $new_page_template || $new_page_template->wp_id ) {
+			update_option( 'has_migrated_' . $page_id, '1' );
+			return;
+		}
+
+		$new_page_template_id = wp_insert_post(
 			[
-				'id'      => 'woocommerce/woocommerce//' . $page_id,
-				'content' => $template_content,
-			]
+				'post_name'    => $new_page_template->slug,
+				'post_type'    => 'wp_template',
+				'post_status'  => 'publish',
+				'tax_input'    => array(
+					'wp_theme' => $new_page_template->theme,
+				),
+				'meta_input'   => array(
+					'origin' => $new_page_template->source,
+				),
+				'post_content' => $template_content,
+			],
+			true
 		);
-		rest_get_server()->dispatch( $request );
-		update_option( 'has_migrated_' . $page_id, '1' );
+
+		if ( ! is_wp_error( $new_page_template_id ) ) {
+			update_option( 'has_migrated_' . $page_id, '1' );
+		}
 	}
 
 	/**
diff --git a/src/Package.php b/src/Package.php
index 4304f189d4e..05efb353e9f 100644
--- a/src/Package.php
+++ b/src/Package.php
@@ -109,7 +109,7 @@ public static function container( $reset = false ) {
 				NewPackage::class,
 				function ( $container ) {
 					// leave for automated version bumping.
-					$version = '10.6.3';
+					$version = '10.6.4';
 					return new NewPackage(
 						$version,
 						dirname( __DIR__ ),
diff --git a/src/Templates/CartTemplate.php b/src/Templates/CartTemplate.php
index af804d10113..ed126951543 100644
--- a/src/Templates/CartTemplate.php
+++ b/src/Templates/CartTemplate.php
@@ -33,7 +33,8 @@ public static function get_placeholder_page() {
 	 */
 	protected function is_active_template() {
 		global $post;
-		return $post instanceof \WP_Post && get_option( 'woocommerce_cart_page_endpoint' ) === $post->post_name;
+		$placeholder = $this->get_placeholder_page();
+		return null !== $placeholder && $post instanceof \WP_Post && $placeholder->post_name === $post->post_name;
 	}
 
 	/**
diff --git a/src/Templates/CheckoutTemplate.php b/src/Templates/CheckoutTemplate.php
index c69df17f9c4..000c6edbe18 100644
--- a/src/Templates/CheckoutTemplate.php
+++ b/src/Templates/CheckoutTemplate.php
@@ -42,6 +42,7 @@ public static function get_template_title() {
 	 */
 	public function is_active_template() {
 		global $post;
-		return $post instanceof \WP_Post && get_option( 'woocommerce_checkout_page_endpoint' ) === $post->post_name;
+		$placeholder = $this->get_placeholder_page();
+		return null !== $placeholder && $post instanceof \WP_Post && $placeholder->post_name === $post->post_name;
 	}
 }
diff --git a/woocommerce-gutenberg-products-block.php b/woocommerce-gutenberg-products-block.php
index fd932a7c57f..87eda68b6ca 100644
--- a/woocommerce-gutenberg-products-block.php
+++ b/woocommerce-gutenberg-products-block.php
@@ -3,7 +3,7 @@
  * Plugin Name: WooCommerce Blocks
  * Plugin URI: https://github.com/woocommerce/woocommerce-gutenberg-products-block
  * Description: WooCommerce blocks for the Gutenberg editor.
- * Version: 10.6.3
+ * Version: 10.6.4
  * Author: Automattic
  * Author URI: https://woocommerce.com
  * Text Domain:  woo-gutenberg-products-block