We have fixed the issue. Our template was based on slick. We compared this to Persona and found differences:
In Slick:
<li component="user/logout">
<a href="#"><i class="fa fa-fw fa-sign-out"></i><span> [[global:logout]]</span></a>
</li>
In Persona:
<li component="user/logout">
<form method="post" action="{relative_path}/logout">
<input type="hidden" name="_csrf" value="{config.csrf_token}">
<input type="hidden" name="noscript" value="true">
<button type="submit" class="btn btn-link">
<i class="fa fa-fw fa-sign-out"></i><span> [[global:logout]]</span>
</button>
</form>
</li>
