diff -u b/core/modules/layout_builder/layout_builder.module b/core/modules/layout_builder/layout_builder.module
--- b/core/modules/layout_builder/layout_builder.module
+++ b/core/modules/layout_builder/layout_builder.module
@@ -159,7 +159,7 @@
   // If the entity is displayed within a Layout Builder block and the current
   // route is in the Layout Builder UI, then remove all contextual link
   // placeholders.
-  if ($display instanceof LayoutBuilderEntityViewDisplay && strpos($route_name, 'layout_builder.') === 0) {
+  if ($display instanceof LayoutBuilderEntityViewDisplay && str_starts_with($route_name, 'layout_builder.')) {
     unset($build['#contextual_links']);
   }
 }
@@ -224,8 +224,8 @@
   // 3. A layout override field is present.
   // @todo Remove instanceof FieldableEntityInterface check in
   //   https://www.drupal.org/node/3046216
-  if (strpos($route_name, 'layout_builder.') !== 0 && $entity instanceof FieldableEntityInterface && $entity->hasField('layout_builder__layout')) {
-    // If an entity's field values change and it also has a layout override in
+  if ($route_name && !str_starts_with($route_name, 'layout_builder.') && $entity instanceof FieldableEntityInterface && $entity->hasField('layout_builder__layout')) {
+    // If an entity's field values change, and it also has a layout override in
     // the tempstore, the tempstore must be updated to reflect those new
     // values.
     /** @var \Drupal\layout_builder\LayoutOverrideFieldHelper $override_field_helper */
diff -u b/core/modules/layout_builder/tests/src/FunctionalJavascript/FieldValuesTest.php b/core/modules/layout_builder/tests/src/FunctionalJavascript/FieldValuesTest.php
--- b/core/modules/layout_builder/tests/src/FunctionalJavascript/FieldValuesTest.php
+++ b/core/modules/layout_builder/tests/src/FunctionalJavascript/FieldValuesTest.php
@@ -53,11 +53,8 @@
     ]));
 
     // Enable layout builder.
-    $this->drupalPostForm(
-      static::FIELD_UI_PREFIX . '/display/default',
-      ['layout[enabled]' => TRUE],
-      'Save'
-    );
+    $this->drupalGet(static::FIELD_UI_PREFIX . '/display/default');
+    $this->submitForm(['layout[enabled]' => TRUE], 'Save');
 
     $this->createNode([
       'type' => 'bundle_for_testing_fields',
@@ -76,11 +73,8 @@
     $assert_session = $this->assertSession();
     $page = $this->getSession()->getPage();
 
-    $this->drupalPostForm(
-      static::FIELD_UI_PREFIX . '/display/default',
-      ['layout[allow_custom]' => TRUE],
-      'Save'
-    );
+    $this->drupalGet(static::FIELD_UI_PREFIX . '/display/default');
+    $this->submitForm(['layout[allow_custom]' => TRUE], 'Save');
 
     $this->drupalGet('node/1');
     $assert_session->pageTextContains('The initial value');
@@ -100,11 +94,9 @@
     $assert_session->pageTextContains($overridden_label);
 
     $changed_body_value = 'The changed value';
-    $this->drupalPostForm(
-      'node/1/edit',
-      ['body[0][value]' => $changed_body_value],
-      'Save'
-    );
+
+    $this->drupalGet('node/1/edit');
+    $this->submitForm(['body[0][value]' => $changed_body_value], 'Save');
 
     // Confirm that changes to a field are seen in the Layout UI without
     // altering a layout's changes in the tempstore.