I have a problem where everytime i join a Lobby a XML-File-Error appears. Every other friend who joins the lobby doesnt have the Problem so it cant be host. And the Error desyncs the game. And in game somethings arent available for example some Diplomacy-Options

Go to the steam directory of ES2, and delete the "Public" folder, then verify you game. Hopefully this fixes it.

Any hint about your OS and rig you make use of?