.../media/js/plugins/drupalmedia/plugin.es6.js     |  2 ++
 .../modules/media/js/plugins/drupalmedia/plugin.js |  2 ++
 .../CKEditorIntegrationTest.php                    | 22 +---------------------
 3 files changed, 5 insertions(+), 21 deletions(-)

diff --git a/core/modules/media/js/plugins/drupalmedia/plugin.es6.js b/core/modules/media/js/plugins/drupalmedia/plugin.es6.js
index d9723095ef..d741dbb2e3 100644
--- a/core/modules/media/js/plugins/drupalmedia/plugin.es6.js
+++ b/core/modules/media/js/plugins/drupalmedia/plugin.es6.js
@@ -486,6 +486,8 @@
           const dataToHash = CKEDITOR.tools.clone(data);
           // The caption does not need rendering.
           delete dataToHash.attributes['data-caption'];
+          // The media entity's label is server-side data and cannot be modified by the content author.
+          delete dataToHash.label;
           // Changed link destinations do not affect the visual preview.
           if (dataToHash.link) {
             delete dataToHash.link.href;
diff --git a/core/modules/media/js/plugins/drupalmedia/plugin.js b/core/modules/media/js/plugins/drupalmedia/plugin.js
index 9178bd995c..01df58af58 100644
--- a/core/modules/media/js/plugins/drupalmedia/plugin.js
+++ b/core/modules/media/js/plugins/drupalmedia/plugin.js
@@ -318,6 +318,8 @@
 
           delete dataToHash.attributes['data-caption'];
 
+          delete dataToHash.label;
+
           if (dataToHash.link) {
             delete dataToHash.link.href;
           }
diff --git a/core/modules/media/tests/src/FunctionalJavascript/CKEditorIntegrationTest.php b/core/modules/media/tests/src/FunctionalJavascript/CKEditorIntegrationTest.php
index 068378b001..caa4b29507 100644
--- a/core/modules/media/tests/src/FunctionalJavascript/CKEditorIntegrationTest.php
+++ b/core/modules/media/tests/src/FunctionalJavascript/CKEditorIntegrationTest.php
@@ -249,7 +249,7 @@ public function testPreviewUsesDefaultThemeAndIsClientCacheable() {
     // a second request is sent. This second request should have transferred 0
     // bytes: the browser should have cached the response, thus resulting in a
     // much better user experience.
-    $this->assertGreaterThan(500, $this->getInitialPreviewRequestTransferSize());
+    $this->assertGreaterThan(500, $this->getLastPreviewRequestTransferSize());
     $this->pressEditorButton('source');
     $this->assertNotEmpty($assert_session->waitForElement('css', 'textarea.cke_source'));
     $this->pressEditorButton('source');
@@ -1363,26 +1363,6 @@ protected function closeDialog() {
     $this->assertTrue($result);
   }
 
-  /**
-   * Gets the transfer size of the initial preview request.
-   *
-   * @return int
-   *   The size of the bytes transferred.
-   */
-  protected function getInitialPreviewRequestTransferSize() {
-    $this->getSession()->switchToIFrame();
-    $javascript = <<<JS
-(function(){
-  return window.performance
-    .getEntries()
-    .filter(function (entry) {
-      return entry.initiatorType == 'xmlhttprequest' && entry.name.indexOf('/media/test_format/preview') !== -1 && entry.nextHopProtocol == 'http/1.1';
-    })[0].transferSize;
-})()
-JS;
-    return $this->getSession()->evaluateScript($javascript);
-  }
-
   /**
    * Gets the transfer size of the last preview request.
    *