Basically, I have a nordic ruin here and when I type "coc lokirstomb" and I enter the dungeon and some parts of the walls and floors are gone.

Items like potions, weapons, gold are all there. Even static items like containers and furniture.

I do not have permission to post links so I can't show you

I just answered another post like this as well. It would seem the nordic ruin interior set is giving a lot of people issues. I had this issue as well with the nordic set and with one piece in the green caves set. The only fix I could find was deleteing the problematic pieces and replacing them with new, but identical, pieces.