I will look into this when I have a moment. Just to check, are you running the latest version of ULX and ULib from
our GitHub page?
UTeam is bundled with ULX/ULib, and has been for some time, but it only is activated on Sandbox. Which gamemode are you running?
Does this happen every time you update/remove a group, or only sometimes? Can you see if it only happens when you update/remove a group that has existing players in it?