I've been observing this behavior quite often, that the game doesn't seem to be really enforcing the set 2 max team difference on the server. This is distinguished from the case when players from one team leave and results in imbalance. In my cases, I'm seeing fresh joiners go straight into the bigger team resulting in more than 2 or more players than the other. I suspect this might have to do with the team swap cool down being enforced wrongly at the moment they join. Please look into it.