Form Theming doesn't work with templates rendered by pugxmultiuserbundle

Question

I'm using Symfony3. I have a separate template for theming forms, it works good in all forms in all templates but it doesn't work with the forms inside the templates rendered by pugxmultiuserbundle

I have created an action for test and I have rendered etudiant.form.html.twig with the form theming and it works good , but as I have said above , if it is rendered by pugxmultiuserbundle the theme doesn't work

template:

{% form_theme form ':Frontend/form:fields.html.twig' %}

    {{ form_start(form, {'method': 'post', 'action': path('etudiant_registration'), 'attr': {'class': 'fos_user_registration_register'}}) }}

     {{ form_widget(form) }}

    <div>
         <input type="submit" value="{{ 'registration.submit'|trans }}"/>
    </div>
 {{ form_end(form) }}

config

pugx_multi_user:
  users:
    etudiant:
        entity:
          class: AppBundle\Entity\Etudiant
        registration:
          form:
            type: AppBundle\Form\User\RegistrationEtudiantFormType
          template: FOSUserBundle:Registration:etudiant.form.html.twig
        profile:
          form:
            type: AppBundle\Form\User\ProfileEtudiantFormType

 # aothers entities