I don't know what is going on here, but my moderators cannot remove groups they have assigned.
Head admins can remove or add any groups and is the highest permission.
Senior moderator is supposed to be able to remove and add 65 or 60 needed group permissions
Senior moderator can add the group, but can not remove it after adding.
Apex legends group is a sample group that he can add but can't remove. It's not meant to be much more than just a group showing that a user is playing this game.

They do have i_group_member_remove_power higher than i_group_needed_member_remove_power for the groups they assigned.
Here are screenshots showing the permissions:

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