AssertionError: The container was serialized.

On Ajax call in form I have error AssertionError: The container was serialized..
Reason: class \Drupal\simple_sitemap_engines\Form\Handler\EntityFormHandler adds submit handler in
ParagraphsWidget instance
in $data["field_my"]["widget"][0]['top']['actions']['actions']['edit_button']['#submit'].

Hotfix workaround: add use DependencySerializationTrait; in ParagraphsWidget.