diff -u b/core/modules/file/file.es6.js b/core/modules/file/file.es6.js
--- b/core/modules/file/file.es6.js
+++ b/core/modules/file/file.es6.js
@@ -62,6 +62,9 @@
    *   Detaches auto file upload trigger.
    */
   Drupal.behaviors.fileAutoUpload = {
+    attach(context) {
+      $(context).find('input[type="file"]').once('auto-file-upload').on('change.autoFileUpload', Drupal.file.triggerUploadButton);
+    },
     detach(context, setting, trigger) {
       if (trigger === 'unload') {
         $(context).find('input[type="file"]').removeOnce('auto-file-upload').off('.autoFileUpload');
@@ -83,12 +86,14 @@
     attach(context) {
       const $context = $(context);
       $context.find('.js-form-submit').on('mousedown', Drupal.file.disableFields);
-      $context.find('.js-form-managed-file .js-form-submit').on('mousedown', Drupal.file.triggerUploadButton);
+      $context.find('.js-form-managed-file .js-form-submit').on('mousedown', Drupal.file.progressBar);
     },
     detach(context) {
-      const $context = $(context);
-      $context.find('.js-form-submit').off('mousedown', Drupal.file.disableFields);
-      $context.find('.js-form-managed-file .js-form-submit').off('mousedown', Drupal.file.triggerUploadButton);
+      if (trigger === 'unload') {
+        const $context = $(context);
+        $context.find('.js-form-submit').off('mousedown', Drupal.file.disableFields);
+        $context.find('.js-form-managed-file .js-form-submit').off('mousedown', Drupal.file.progressBar);
+      }
     },
   };
 
@@ -164,8 +169,7 @@
      *   The event triggered. For example `change.autoFileUpload`.
      */
     triggerUploadButton(event) {
-      Drupal.file.progressBar(event);
-      $(event.target).closest('.js-form-managed-file').find('.js-form-submit').trigger('fileUpload');
+      $(event.target).closest('.js-form-managed-file').find('.js-form-submit').trigger('mousedown');
     },
 
     /**
@@ -215,7 +219,7 @@
      *   The event triggered, most likely a `mousedown` event.
      */
     progressBar(event) {
-      const $clickedButton = $(event.target).closest('.js-form-managed-file').find('.js-form-submit');
+      const $clickedButton = $(this);
       const $progressId = $clickedButton.closest('div.js-form-managed-file').find('input.file-progress');
       if ($progressId.length) {
         const originalName = $progressId.attr('name');
@@ -232,6 +236,7 @@
       setTimeout(() => {
         $clickedButton.closest('div.js-form-managed-file').find('div.ajax-progress-bar').slideDown();
       }, 500);
+      $clickedButton.trigger('fileUpload');
     },
 
     /**
diff -u b/core/modules/file/file.js b/core/modules/file/file.js
--- b/core/modules/file/file.js
+++ b/core/modules/file/file.js
@@ -36,6 +36,9 @@
   };
 
   Drupal.behaviors.fileAutoUpload = {
+    attach: function attach(context) {
+      $(context).find('input[type="file"]').once('auto-file-upload').on('change.autoFileUpload', Drupal.file.triggerUploadButton);
+    },
     detach: function detach(context, setting, trigger) {
       if (trigger === 'unload') {
         $(context).find('input[type="file"]').removeOnce('auto-file-upload').off('.autoFileUpload');
@@ -47,12 +50,14 @@
     attach: function attach(context) {
       var $context = $(context);
       $context.find('.js-form-submit').on('mousedown', Drupal.file.disableFields);
-      $context.find('.js-form-managed-file .js-form-submit').on('mousedown', Drupal.file.triggerUploadButton);
+      $context.find('.js-form-managed-file .js-form-submit').on('mousedown', Drupal.file.progressBar);
     },
     detach: function detach(context) {
-      var $context = $(context);
-      $context.find('.js-form-submit').off('mousedown', Drupal.file.disableFields);
-      $context.find('.js-form-managed-file .js-form-submit').off('mousedown', Drupal.file.triggerUploadButton);
+      if (trigger === 'unload') {
+        var $context = $(context);
+        $context.find('.js-form-submit').off('mousedown', Drupal.file.disableFields);
+        $context.find('.js-form-managed-file .js-form-submit').off('mousedown', Drupal.file.progressBar);
+      }
     }
   };
 
@@ -87,8 +92,7 @@
       }
     },
     triggerUploadButton: function triggerUploadButton(event) {
-      Drupal.file.progressBar(event);
-      $(event.target).closest('.js-form-managed-file').find('.js-form-submit').trigger('fileUpload');
+      $(event.target).closest('.js-form-managed-file').find('.js-form-submit').trigger('mousedown');
     },
     disableFields: function disableFields(event) {
       var $clickedButton = $(this).findOnce('ajax');
@@ -109,7 +113,7 @@
       }, 1000);
     },
     progressBar: function progressBar(event) {
-      var $clickedButton = $(event.target).closest('.js-form-managed-file').find('.js-form-submit');
+      var $clickedButton = $(this);
       var $progressId = $clickedButton.closest('div.js-form-managed-file').find('input.file-progress');
       if ($progressId.length) {
         var originalName = $progressId.attr('name');
@@ -124,6 +128,7 @@
       setTimeout(function () {
         $clickedButton.closest('div.js-form-managed-file').find('div.ajax-progress-bar').slideDown();
       }, 500);
+      $clickedButton.trigger('fileUpload');
     },
     openInNewWindow: function openInNewWindow(event) {
       event.preventDefault();
diff -u b/core/modules/file/src/Element/ManagedFile.php b/core/modules/file/src/Element/ManagedFile.php
--- b/core/modules/file/src/Element/ManagedFile.php
+++ b/core/modules/file/src/Element/ManagedFile.php
@@ -227,6 +227,8 @@
         ],
       ],
       'wrapper' => $ajax_wrapper_id,
+      // Set a custom submit event so we can modify the upload progress
+      // identifier element before the form gets submitted.
       'event' => 'fileUpload',
       'effect' => 'fade',
       'progress' => [
@@ -240,6 +242,7 @@
       '#name' => $parents_prefix . '_upload_button',
       '#type' => 'submit',
       '#value' => t('Upload'),
+      '#attributes' => ['class' => ['js-hide']],
       '#validate' => [],
       '#submit' => ['file_managed_file_submit'],
       '#limit_validation_errors' => [$element['#parents']],