Player characters and follow thralls sinking waist deep into mesh. Often the game attempts to correct itself, unsuccessfully, and makes the player character “fly” above the mesh, animated as though falling.
Problem most severe immediately following game launch, clears up somewhat when moving outside render range and then returning
Wooden foundations used to be the worst at this, but it happened with certain tier 3 foundations and especially ceilings too. I never had this happen on any sandstone surface or the ingame world outside of player-made buildings though, and this applies to 2017-2020 across various patches. Mind you this was PC/EU Official.