I watched that phenomenon too !
In coop games it happens from time to time.
I have no idea what triggers that and if it is reproducable but it happened to me twice that a Bot suddenly dissapeared.
All you can do in that situation is runing behind hard cover as quick as possible and listen to the walking sounds.
The Bot will be visible again and try to attack or flank as they always do.
@chaton unfortunately not; my rig would probably burn up if I tried that; I just so manage to run stable 60fps w/o recording or streaming.
another nice feat I saw recently was a bot that would shoot at me while going down into "the underworld" as if in an escalator (lift). it looked exactly like a 3rd person perspective of what happens to your player character once in a while