Thanks for the repro steps. I was able to reproduce this using the latest Mirror Asset Store release, 30.2.2.
after they connect, exit one of them => both are brought to the main menu
Just a note on that part - this only happens if you disconnect the master client hosting the game. Disconnecting a client does not stop the master from continuing playing.
In the OnClientDisconnect method in the NetworkManagerCustom script, I tried adding a "hard" disconnect using StopHost() like this:
//switch from the online to the offline scene after connection is closed
if (!NetworkManager.IsSceneActive(offlineScene))
{
StopHost();
SceneManager.LoadScene(offlineScene);
}
else
CreateMatch();
When testing, 10 out of 10 times the issue you mentioned did not occur anymore. However there was a rare issue when starting a game on both applications at the same time, both clients would think they are the master, but actually land in the same room. Please let me know if you experience that issue at some point. Usually, this should not happen as you would not try to start multiple instances as a host on the same device.