RadioField Fieldlist validation not working

I am trying to do validation of a FieldList which includes multiple RadioField I also tried the validation setup described here: https://github.com/wtforms/wtforms/issues/477 This is working and I have to select one of the radio buttons to submit. The form.validate_on_submit() condition is however never matched.

My forms:

class SelectRole(FieldsRequiredForm):
    radio_group = RadioField(choices=[('one', 'Role_1'), ('two', 'Role_2'), ('three', 'Role_3'), ('four', 'Role_4')])

class RoleGroupMapping(FlaskForm):
    role = FieldList(FormField(SelectRole), min_entries=1)
    submit = SubmitField('Submit')

my view:

@app.route('/role_database', methods=['GET', 'POST'])
@login_required
def role_management_page():
    form = RoleGroupMapping()
    if form.validate():
        print('FORM VALID')
    else:
        print('not validated')
    return render_template('role_database.html', title='Role Database', form=form)

my html template:

{% extends "layout.html" %}
{% block content %}
<div class="row justify-content-center">
    <div class="col-lg">
        <div class="content-section">
            <h3 class="mt-5">Group Mapping</h3>
            <form action="" method="POST">
                {{ form.hidden_tag() }}
                {% for entry in form.role %}
                    <div class="row mt-2">
                        <div class="col">Role_XXX</div>
                        {% for radio_button in entry.radio_group %}
                            <div class="col">
                                {{ radio_button }}
                                {{ radio_button.label }}
                            </div>
                        {% endfor %}
                    </div>
                {% endfor %}
                <div class="form-group">
                    {{ form.submit(class="btn btn-outline-primary mt-3") }}
                </div>
            </form>
        </div>
    </div>
</div>
{% endblock content %}