That's odd... I haven't seen that before. This might be worth sending a ticket into Client Care... hopefully they can see what is happening on that account (possibly an old, and maybe corrupted "custom landing page" selection - that used to be something each user could control).
Client Care may need to do a screenshare with the user, and might need to walk them through getting the HAR recording of their session so they can see what all is happening client side.
Good luck getting that fixed.
