Create nodes unlimited times
For some weird reason the Ajax response wasn't updating the form_build_id value and the request takes it as the same form, so I added a new Ajax Command: 

function saveAjaxForm(&amp;$form, FormStateInterface $form_state) {
  $old_form_build_id = $form['#build_id'];
  $new_form_build_id = $old_form_build_id.rand();

  $response = new AjaxResponse();

  $response-&gt;addCommand(new UpdateBuildIdCommand($old_form_build_id, $new_form_build_id));
  $response-&gt;addCommand(new AlertCommand('Saved'));

  return $response;
}


It solves the issue.