Holseher’s Tower. It is a known issue by now.
Waiting for hotfix. Not necessarily game breaking but pretty annoying.
Holsher’s Tower - Vermintide 2 / Vermintide 2 - Bugs - Fatshark Forums (fatsharkgames.com)
The ground is missing - Vermintide 2 / Vermintide 2 - Bugs - Fatshark Forums (fatsharkgames.com)
I think there is one with a screenshot somewhere as well. So yea, it should get fixed.