diff -u b/core/tests/Drupal/FunctionalJavascriptTests/Core/Form/FormGroupingElementsTest.php b/core/tests/Drupal/FunctionalJavascriptTests/Core/Form/FormGroupingElementsTest.php
--- b/core/tests/Drupal/FunctionalJavascriptTests/Core/Form/FormGroupingElementsTest.php
+++ b/core/tests/Drupal/FunctionalJavascriptTests/Core/Form/FormGroupingElementsTest.php
@@ -37,6 +37,7 @@
    */
   public function testVerticalTabChildVisibility() {
     $session = $this->getSession();
+    $web_assert = $this->assertSession();
 
     // Request the group vertical tabs testing page with a fragment identifier
     // to the second element.
@@ -60,15 +61,15 @@
     // inactive vertical tab.
     $session->executeScript("jQuery('<a href=\"$child_1_selector\"></a>').insertAfter('h1')[0].click()");
 
-    // Assert that the child in the first vertical tab is visible.
-    $this->assertTrue($child_1->isVisible(), 'Child 1 is visible after a fragment link click');
+    // Assert that the child in the first vertical tab becomes visible.
+    $web_assert->waitForElementVisible('css', $child_1_selector, 50);
 
     // Trigger a URI fragment change (hashchange) to show the second vertical
     // tab again.
     $session->executeScript("location.replace('$child_2_selector')");
 
-    // Assert that the child in the second vertical tab is visible again.
-    $this->assertTrue($child_2->isVisible(), 'Child 2 is visible after a fragment change');
+    // Assert that the child in the second vertical tab becomes visible again.
+    $web_assert->waitForElementVisible('css', $child_2_selector, 50);
 
     $tab_link_1->click();
 
@@ -86,6 +87,7 @@
    */
   public function testDetailsChildVisibility() {
     $session = $this->getSession();
+    $web_assert = $this->assertSession();
 
     // Store reusable JavaScript code to remove the current URI fragment and
     // close all details.
@@ -108,8 +110,8 @@
     // elements of the child.
     $session->executeScript("location.replace('$child_selector')");
 
-    // Assert that the child is visible again.
-    $this->assertTrue($child->isVisible(), 'Child became visible after a fragment change');
+    // Assert that the child becomes visible again after a hash change.
+    $web_assert->waitForElementVisible('css', $child_selector, 50);
 
     $session->executeScript($reset_js);
 
@@ -117,8 +119,8 @@
     // details element.
     $session->executeScript("jQuery('<a href=\"$child_selector\"></a>').insertAfter('h1')[0].click()");
 
-    // Assert that the child is visible again.
-    $this->assertTrue($child->isVisible(), 'Child became visible after a fragment link click');
+    // Assert that the child is visible again after a fragment link click.
+    $web_assert->waitForElementVisible('css', $child_selector, 50);
 
     // Find the summary belonging to the closest details element.
     $summary = $page->find('css', '#edit-meta > summary');