NAS542 Help is Empty

Titule

On the NAS542-Desktop, there is a Help-Application ("Hilfe", it's the German UI).

Clicking it opens a new browser-tab (URL: http://zyxelnas/r51163,/desktop,/Help/wwhelp/wwhimpl/js/html/wwhelp.htm#context=Help&topic=Desktop) which is totally empty (besides a window-split from top to button on the left side).

Tried it on firefox and edge.

Looks like a configuration problem, how can I solve it?

#NAS_Mar_2019