Ticket #42614: 42614.0.diff

src/wp-includes/class-wp-customize-manager.php

@@ -893 +893 @@
          */
         public function wp_loaded() {
 
+                if ( $this->changeset_post_id() && 'trash' === get_post_status( $this->changeset_post_id() ) ) {
+                        return;
+                }
+
                 // Unconditionally register core types for panels, sections, and controls in case plugin unhooks all customize_register actions.
                 $this->register_panel_type( 'WP_Customize_Panel' );
                 $this->register_panel_type( 'WP_Customize_Themes_Panel' );