The graphics for some of the floors and walls are missing in the fourth and fifth islands in the Treasures of the Midnight Isles DLC. It is some, but not all, of the wooden planking. I think all of the ramps. The characters look like they are walking on thin air. I checked youtube playthrough videos to make sure what i suspected should be there should be there.
I’m playing the DLC as part of the campaign. On a Windows machine, through the GoG launcher, if that helps.