diff -u b/core/modules/views_ui/src/ViewPreviewForm.php b/core/modules/views_ui/src/ViewPreviewForm.php
--- b/core/modules/views_ui/src/ViewPreviewForm.php
+++ b/core/modules/views_ui/src/ViewPreviewForm.php
@@ -26,6 +26,9 @@
     $form['#suffix'] = '</div>';
     $form['#id'] = 'views-ui-preview-form';
 
+    // Reset the cache of IDs. Drupal rather aggressively prevents ID
+    // duplication but this causes it to remember IDs that are no longer even
+    // being used.
     Html::resetSeenIds();
 
     $form_state->disableCache();