Loaded up a new scenario from MekHQ/StratCon but I didn't pay attention to the generated OpFor, it was big enough that it locked up MM.272,880 BV1,161 Units - almost entirely infantry and BattleArmorMy force, 6 mechs...
Yeah, there is a bug in pre-50.01 that causes some large APCs to have near infinite capacity. The issue is fixed in 50.01, so it might be worth updating.