Proxy responds with " Whoops, looks like something went wrong."

I searched for lieferdienst schwarzenbek. Since the selected shop was closed in real life, the https://pizzango.de made a kind of overlay above the website and tried to catch my clicks to redirect me to their homepage. Since I just wanted to look through the menus I used the proxy and the first page was shown very well and then I got "Whoops, looks like something went wrong." when clicking on Pizza.

The error message doesn't explain very much. It would be nicer if there would be more details, at least after clicking on "give me more details".

I use Icecat (GNU's version of Firefox) and don't accept many cookies, though I guess I accepted enough. Third party cookies are not allowed. In case it is a problem because of the cookies, then the error message should be another.

Opening Hours in case it is relevant for the error: Mo.-Di.: 11:30 - 14:30 u. 17:00 - 22:15 Uhr Mi: Ruhetag Do.-Sa.: 11:30 - 14:30 u. 17:00 - 22:15 Uhr So. u. Feiertag: 12:00 - 22:15 Uhr

The issue is confidental because I don't want the internet to know where I look at food ;)