There are invisible botters. You cannot see them, you cannot target them, you can only see their actions in the battle log.

No, my game was not glitching, because the bots were hitting mobs (I could see their skills in the battle log) but the mobs just stood there unable to target them back. It wasn't a one-hit kill too so the mobs had plenty of time to move or run towards the attacker if that mob could target the attacker.

I've reported them to SE from in-game, but no reply, not even a "we will look into this blah blah".