Webclient not showing correctly when not on localhost

Hi,

The WebClient at a customer is no longer displaying correctly. If I acces it by localhost it is working fine, but if I access it by the actual hostname it is looking strange. - Any help that could guide me in a direction of a solution is appreciated

Not Working
Image may be NSFW.
Clik here to view.

Working
Image may be NSFW.
Clik here to view.