Unable to connect with friends

Everytime I try to connect to my friends (PS4) world I stuck in the „locating server“ screen until I abort the connection.

I‘ve tried this with several devices like PS5, iOS & iPadOS, but it didn’t work with any of them. All ports needed for PlayStation network and Microsoft live are opened in my router, although  this also doesn’t help. We’ve also tried the workaround stated in another bug by killing my character in the world with a potion. 

Another friend of ours (PS4) is able to connect to his world.