I reported this a while back but it does not appear to have changed:
Monsters with volley attacks, such as the Mancubus or Cyberdemon, will aim down to shoot at the floor, where the monster corpse is, if their first shot killed the enemy - even if they're on the same elevation. This happens in (Strict) compatibility and is not vanilla behaviour. The monster is supposed to keep shooting straight over the corpse where the dead enemy's hitbox used to be and not correct their aim downwards mid-volley like that.
Re: Monsters shooting at corpses
Fri Jan 15, 2021 9:37 pm
Here is a rough video demonstration showing the difference. After the 18 second mark, you can see the GZ Cyber fire shots at the ground after killing Barons. Meanwhile, in the second half, the PR+ Cyber always shoots parallel to the ground after a kill.