Issue #3052574: Facets with AJAX not working in most of situations

src/Controller/FacetBlockAjaxController.php

@@ -10,6 +10,7 @@ use Drupal\Core\Controller\ControllerBase;
 use Drupal\Core\Path\CurrentPathStack;
 use Drupal\Core\PathProcessor\PathProcessorManager;
 use Drupal\Core\Routing\CurrentRouteMatch;
+use Drupal\facets\Plugin\Block\FacetBlock;
 use Symfony\Component\DependencyInjection\ContainerInterface;
 use Symfony\Component\HttpFoundation\Request;
 use Symfony\Component\HttpFoundation\RequestStack;
@@ -168,7 +169,7 @@ class FacetBlockAjaxController extends ControllerBase {
         $block_view = NULL;
         // @todo We should not create an instance if we have already created one.
         $block_instance = $this->blockManager->createInstance($summary_plugin_id);
-        if ($block_instance) {
+        if ($block_instance && $block_instance instanceof FacetBlock) {
           $block_view = $block_instance->build();
           if ($block_view) {
             // Replace content facets summary plugin ID selector.