FS Logix always 15sec Black Screen

We have Win10 2004 Session Hosts with the latest KB and FS Logix Agent installed. I've tried a lot of different registry keys. VHD are on Azure Files Premium.

It doesn't really matter what I do after the initial log in there is a black screen for 15sec exactly. It doesn't matter if the server is full or not. And this happens on both session hosts.

I don't really know where to look anymore for a solution.