diff -r 34716fd837a4 -r be944660c56a wp/wp-includes/blocks/block.php
--- a/wp/wp-includes/blocks/block.php	Tue Dec 15 15:52:01 2020 +0100
+++ b/wp/wp-includes/blocks/block.php	Wed Sep 21 18:19:35 2022 +0200
@@ -13,6 +13,8 @@
  * @return string Rendered HTML of the referenced block.
  */
 function render_block_core_block( $attributes ) {
+	static $seen_refs = array();
+
 	if ( empty( $attributes['ref'] ) ) {
 		return '';
 	}
@@ -22,11 +24,27 @@
 		return '';
 	}
 
+	if ( isset( $seen_refs[ $attributes['ref'] ] ) ) {
+		// WP_DEBUG_DISPLAY must only be honored when WP_DEBUG. This precedent
+		// is set in `wp_debug_mode()`.
+		$is_debug = defined( 'WP_DEBUG' ) && WP_DEBUG &&
+			defined( 'WP_DEBUG_DISPLAY' ) && WP_DEBUG_DISPLAY;
+
+		return $is_debug ?
+			// translators: Visible only in the front end, this warning takes the place of a faulty block.
+			__( '[block rendering halted]' ) :
+			'';
+	}
+
 	if ( 'publish' !== $reusable_block->post_status || ! empty( $reusable_block->post_password ) ) {
 		return '';
 	}
 
-	return do_blocks( $reusable_block->post_content );
+	$seen_refs[ $attributes['ref'] ] = true;
+
+	$result = do_blocks( $reusable_block->post_content );
+	unset( $seen_refs[ $attributes['ref'] ] );
+	return $result;
 }
 
 /**