Network - Changing Scenes Errors

Hello,

I am creating a multiplayer game (1 vs 1) and I seem to have a problem when one player decides to leave the game. If you press Esc you can leave the game and it takes you back to the main menu. But the main menu doesn't work anymore. When I press different buttons it plays the animations wrong and I cannot interact correctly with my UI. Also if the other player leaves too and both are in the main menu, they cannot start a new game anymore. The both have to close the application.

I have read something about SetLevelPrefix but I didn't understand how it works. Can somebody give me a solution for this, what can I do to fix this?

Thank you.