I was using the GameOver handler process for RPC I want to call on Client. In this case, I was trying to call Rpc during the ServerOnBaseSpawned event.
The function was not firing, and googling the problem revealed, that Mirror have to finish a lot of stuff before it can execute RPC’s. I’ve added 3 seconds delayed and it worked.
Now I am wondering what is the correct way of doing this? E.g. showing the screen message to all clients once the game fully functional in the map scene