ArcGIS Enterprise Sites 10.8.1: Error 404 when trying to take a look at dataset for new users

[Martin1]

Hello,

I have created an ArcGIS Enterprise Site to be our Open Data platform.

You can take a look at it here: French / German

The problem is, that if someone visits the site for the first time (or with a cleaned cache) taking a look at a dataset gives an 404 error (see below). The site in itself seems to work fine, it is the access to the data that does not work properly.

Weird is, that if you then click on the link to change the language (which in fact is a link to another site) and then back, it starts to work and the data becomes visible. You should be able to reproduce this behavior, just click on one of the categories and then choose any dataset.  Once it started working, it will keep on working till the next time the cache is cleared. 

Can someone explain to me, what could cause this behavior? It seems that something is not starting properly at first, but once it works it keeps running. 

Thanks for any help. 

[Martin1]

It turned out that if I enable anonymous access to our Portal, it works.

Could this be a bug? It sounds a bit like BUG-000133039 but is certainly not the same. The behaviour is a bit different and we have all Patches installed.