diff -u b/core/modules/comment/src/CommentViewBuilder.php b/core/modules/comment/src/CommentViewBuilder.php
--- b/core/modules/comment/src/CommentViewBuilder.php
+++ b/core/modules/comment/src/CommentViewBuilder.php
@@ -140,19 +140,14 @@
         }
       }
 
-      if ($build[$id]['#comment_threaded']) {
-        // The final comment must close up some hanging divs.
-        $build[$id]['#comment_indent_final'] = $current_indent;
-      }
       // Commented entities already loaded after self::getBuildDefaults().
       $commented_entity = $entity->getCommentedEntity();
-      if (!$commented_entity) {
-        return;
-      }
+      // Set defaults if the commented_entity does not exist.
+      $bundle = $commented_entity ? $commented_entity->bundle() : '';
+      $entity_type_id = $commented_entity ? $commented_entity->getEntityTypeId() === 'node' : NULL;
 
       $build[$id]['#entity'] = $entity;
-      $build[$id]['#theme'] = 'comment__' . $entity->getFieldName() . '__' . $commented_entity->bundle();
-
+      $build[$id]['#theme'] = 'comment__' . $entity->getFieldName() . '__' . $bundle;
       $display = $displays[$entity->bundle()];
       if ($display->getComponent('links')) {
         $build[$id]['links'] = [
@@ -173,7 +168,7 @@
         $build[$id]['#attached'] = [];
       }
       $build[$id]['#attached']['library'][] = 'comment/drupal.comment-by-viewer';
-      if ($attach_history && $commented_entity->getEntityTypeId() === 'node') {
+      if ($attach_history && $entity_type_id) {
         $build[$id]['#attached']['library'][] = 'comment/drupal.comment-new-indicator';
 
         // Embed the metadata for the comment "new" indicators on this node.
@@ -183,6 +178,10 @@
         ];
       }
     }
+    if ($build[$id]['#comment_threaded']) {
+      // The final comment must close up some hanging divs.
+      $build[$id]['#comment_indent_final'] = $current_indent;
+    }
   }
 
   /**
diff -u b/core/modules/comment/src/Entity/Comment.php b/core/modules/comment/src/Entity/Comment.php
--- b/core/modules/comment/src/Entity/Comment.php
+++ b/core/modules/comment/src/Entity/Comment.php
@@ -404,8 +404,9 @@
    * {@inheritdoc}
    */
   public function getAuthorName() {
-    if ($user = $this->get('uid')->entity) {
-        return $user->label();
+    // If their is a valid user id and the user entity exists return the label.
+    if ($this->get('uid')->target_id && $this->get('uid')->entity) {
+      return $this->get('uid')->entity->label();
     }
     return $this->get('name')->value ?: \Drupal::config('user.settings')->get('anonymous');
   }