diff -u b/core/modules/block/block.module b/core/modules/block/block.module
--- b/core/modules/block/block.module
+++ b/core/modules/block/block.module
@@ -280,7 +280,7 @@
 function block_menu_delete(Menu $menu) {
   if (!$menu->isSyncing()) {
     foreach (Block::loadMultiple() as $block) {
-      if ($block->getPlugin() == 'system_menu_block:' . $menu->id()) {
+      if ($block->getPluginId() == 'system_menu_block:' . $menu->id()) {
         $block->delete();
       }
     }