I develop a plugin but I've got a problem when I render sub-menus (added with the hook admin_menu). At the moment of the callback, I render the content with the following:

<div class="wrap">
    <?php $this->render(); ?>
</div>

But I don't know why they are render inside the same content (see attachment). I'm using PHP/MySQL 7.4.2 with theme Sydney Pro in localhost

Thanks in advance