Win10 and Ps4 Crossplatform Issue

Currently I (Win10) want to play with a Friend (Ps4) but he can't join my Realm because it's not available for Ps4... fine. We both use the same version, so the only issue is the one below. 

I created a Singleplayer Map and Invited him, he can join the World, I can see him, staying at the Worlds Spawn, but he stucks in the "locate server screen" all the time. 
I can see him, but hes just loading in the locating screen and can't do anything... (see attached image)

Acutally PS4 is a mess. It seems like you can't join a Server (except of the basic 6), you can't join a realm, only invite and you can't join a friends singleplayer world (well you can but you just stuck in the locating screen). 
probably all of those issues are connected?

Notice: The image below is in German! It means "Searching for Server", so like mentioned above it's stucking in the "locate server" screen.