Incorrect name on AutoTextFields class on ajax_example module 4.0.4 version

Thanks for your work. I forgot to say that textfields_container is incorrect key. We need to update it too

  public function textfieldsCallback($form, FormStateInterface $form_state) {
    return $form[’textfields_container'];
}

That is a different bug from what reported here. I will create a new bug report for that.