Do not use trigger since this.form is a DOM Element and not a jQuery element

wagtail/documents/templates/wagtaildocs/documents/index.html

@@ -12,7 +12,7 @@
 
         $(function() {
             $('#collection_chooser_collection_id').on('change', function() {
-                this.form.trigger('submit');
+                this.form.submit();
             })
         });
     </script>

wagtail/images/templates/wagtailimages/images/index.html

@@ -14,7 +14,7 @@
 
         $(function() {
             $('#collection_chooser_collection_id').on('change', function() {
-                this.form.trigger('submit');
+                this.form.submit();
             })
         });
     </script>