Super Gore Nest master level softlocks

[Tripitaka (HUN)]

The last arena fight with 4 tyrants and 3 archviles when reaches it's final stage when I play, continually starts spawning imps, and there are no heavy demons to kill on the map, except for a few in an unreachable position.
The secret room, where the slayer key is supposed to be on the original level is unreachable from any place, not even with trying to meathook up there. There are two cyber mancubi, which refuse to go down, making progress impossible.

I've restarted this encounter and completed it again, and it happened again. It happens 100% every time.

Have any of you encountered this bug? Do you know how to fix this?

[Bresker]

Yep ! had this problem yesterday, you can obtain a BFG ammo in that area , it is kind of hidden you need to find the crack in the wall, anw when i had that problem i shot my BFG one last time in the middle of the map from the side(to maximize the projectile distance) and the tendrils killed these these fcker.

[Tripitaka (HUN)]

So you are expected to have a BFG after *that* arena fight?!
This is madness.

[Laciiijeeee]

Same thing happened to me, already used all my BFG, I was kiling imps for like 10 minutes, but then I managed to meathook up there and I found this. I killed it with the ballista and then the arena ended.

https://steamcommunity.com/sharedfiles/filedetails/?id=2306328963