Asylum of the Fiends:
In the side passages of this vault, the first walls on the player left and right are missing textures. The walls just appear black-ish. This occurs on most of the side passages.
Refuge of the Gremlins:
Both Grumblin vaults, maybe some “drowned”? Step on the floor switch and enter. The left and right walls are missing textures. They are also black-ish.