So the bug affected all mobs which is really bad, the mob skin VISIBLY will standing motionless while the actual mob is roaming like normal, you can't see the roaming one so I called them ghost or something, the only way to kill this mob is to find their motionless SKIN, but the chance that you can even hit it a bit small and not even worth to spend the time. There's no trigger for this one and I assuming that the bug will immediately activated after the game started.
P.s. the mob have a chance to pick up an item that they shouldn't have (Skeleton pick up droped Iron Sword).