Can´t Join local Session with Subsystem Null!?

I´m running with Blueprints for sessionmaking.
I set the Player Number to 2 and start New Window (PIE).

It doesn´t matter if i check or uncheck LAN, it can´t find the created Session.
I checked the Log, too. Host is active and no “connection lost”.

I also checked, if a VirtualNetwork is active. But i´ve non installed. Kaspersky, Windows and my Router are forwarding and not blocking…