Please test completely mod/CC free. See the instructions for vanilla testing in How to Use Mods and CC
Please note that some mods that commonly cause this sort of issue cannot be named in these forums due to changing the game rating, which is for 13-year-olds up.
I have tested without mods/cc and then the sitting was working.
Jusu12345 You can check the Broken and Updated Mods and CC thread, but if you use 18+ mods, you'll need to check with their creators for information.
Instructions on how to narrow down a broken mod are in How to Use Mods and CC
