Connection via Steam crashes - Multiplayer help

alt textHi everyone,

I followed this tutorial Blueprint Multiplayer: Find a Match Graph | 11 | v4.11 Tutorial Series | Unreal Engine - YouTube to get a Multiplayer System via Internet / LAN by using Steam.

I have two PCs, two Steam Accounts, enabled Steam-Plugin in UE and added the missing lines in DefaultGame.ini.
The Host-PC can host a Game (internet) and start the game (everything works well at this point).
The Client-PC can open Menu, choose “Find a Match”, the connection is found, but when I click “Accept” the Client doesnt connect but it crashes and shows the error message attached. The Host doenst crash.

I use Blueprints and want to solve the case hopefully only with blueprints.
Someone else knows why this happens? And how to fix?

Regards november92