288 is the limit per side, with 95 to 100 players and none of the created groups actually do delete, probably fucked:
when you are in no group, you are technically in a group of your own
all AI/Frozen units such as gas station, drug runner, medical all have their own groups, whome are side civilian
All the created groups are still there that players are not in, likely including gang groups that were created
By moving all of the AI/Frozen units from side civilian to side opfor would open more slots for the civilian side, and cleaning up the created groups would stop the connecting of players looking for a group, then arma realizing that there is no more room, and you get put in a random group or gang group that you never joined, simply because the limit maxed out
there is no "cleanup"