Thank you for the update. I will also update if I experience anything else regarding this bug (or others if they come up).
Hold the boat, has this issue been fixed in 1.4.3 beta branch?
Which one are you referring to? The slit visible from behind the model or the mutant model?
You can't use newer files in an older version, just doesn't work like that. Simply put there are a plethora of variables that were changed on the character level that make the saves incompatible. You can only bring them forward. I rolled back to a save that I intentionally backed up in the case something went wrong. I rolled backed because I wanted to make sure I got the optimal multiplayer experience (more people on the main build than the beta).
Indeed, as I suggested above you need to delete your files that are under the 1.1 beta. If you try to resume in 1.0.10 with 1.1 save files present the game will crash.
You don't need to do a fresh install (although if you wish to do so there is nothing wrong). I have switched back and fourth and as long as the beta saves are removed the switch is seamless (granted I also go a bit overkill whenever I opt into betas and make an absurd amount of previous version backups). However, if I am not mistaken you are not able to downgrade any file back to a prior version. You can only go forward (ex 1.0.10 to 1.1).