Do a search of your theme template for hooking into the admin menu. Something like:
add_action('admin_menu', 'function_name');
Then look at any functions that are hooked.
This may be a pain, but you can usually get to the ACF page by entering the URL directly in the location bar:
http://www.yoursite.com/wp-admin/edit.php?post_type=acf
If you can’t access it that way then the permissions needed to access the page have been changed for your user type. Maybe there is a plugin installed that adds controls for who can access what.
