Try adjusting your max frame rate. Minecrafts original settings should have it set to 60fps. No clue why it would only happen in the lobby though, lobbies normally cause a fps drop, I'll drop to 70-80 in the lobby, while I run 115-120 in a game.anyone else know to problem that you just can't get more than 60fps in a lobby?
If it really bothers you, you should set ‘Player visibility’ to ‘No one’ or ‘Friends + Party’, helps a lot!anyone else know to problem that you just can't get more than 60fps in a lobby?