diff -u b/core/modules/views/lib/Drupal/views/DisplayArray.php b/core/modules/views/lib/Drupal/views/DisplayArray.php
--- b/core/modules/views/lib/Drupal/views/DisplayArray.php
+++ b/core/modules/views/lib/Drupal/views/DisplayArray.php
@@ -130,7 +130,8 @@
    * Implements \Iterator::key().
    */
   public function key() {
-    return key($this->displayIDs);
+    $key = key($this->displayIDs);
+    return $key;
   }
 
   /**
@@ -145,7 +146,7 @@
    * Implements \Iterator::rewind().
    */
   public function rewind() {
-    reset($this->displayHandlers);
+    reset($this->displayIDs);
   }
 
   /**