Fix You attempted to edit an item that doesn't exist error on WordPress 5.8

src/BlockTemplatesController.php

@@ -92,9 +92,10 @@ public function maybe_return_blocks_template( $template, $id, $template_type ) {
 
 		// Check if the theme has a saved version of this template before falling back to the woo one. Please note how
 		// the slug has not been modified at this point, we're still using the default one passed to this hook.
-		$maybe_template = function_exists( 'get_block_template' ) ?
-			get_block_template( $id, $template_type ) :
-			gutenberg_get_block_template( $id, $template_type );
+		$maybe_template = function_exists( 'gutenberg_get_block_template' ) ?
+			gutenberg_get_block_template( $id, $template_type ) :
+			get_block_template( $id, $template_type );
+
 		if ( null !== $maybe_template ) {
 			add_filter( 'pre_get_block_file_template', array( $this, 'maybe_return_blocks_template' ), 10, 3 );
 			return $maybe_template;
@@ -103,9 +104,9 @@ public function maybe_return_blocks_template( $template, $id, $template_type ) {
 		// Theme-based template didn't exist, try switching the theme to woocommerce and try again. This function has
 		// been unhooked so won't run again.
 		add_filter( 'get_block_file_template', array( $this, 'get_single_block_template' ), 10, 3 );
-		$maybe_template = function_exists( 'get_block_template' ) ?
-			get_block_template( 'woocommerce//' . $slug, $template_type ) :
-			gutenberg_get_block_template( 'woocommerce//' . $slug, $template_type );
+		$maybe_template = function_exists( 'gutenberg_get_block_template' ) ?
+			gutenberg_get_block_template( 'woocommerce//' . $slug, $template_type ) :
+			get_block_template( 'woocommerce//' . $slug, $template_type );
 
 		// Re-hook this function, it was only unhooked to stop recursion.
 		add_filter( 'pre_get_block_file_template', array( $this, 'maybe_return_blocks_template' ), 10, 3 );