There have been reports that rejoining games isn't possible sometimes, as the rating for the player rejoining the lobby doesn't show up (https://gitea.wildfiregames.com/0ad/0ad/issues/7185). There was already some discussion regarding this topic in the following thread: Analysis of logs for cases where that happened to players showed that in these cases the players show up as connected with two different instances of 0ad to the lobby server. As we can assume they didn't do that intentional