New startup error in 9.1.1

I decided to upgrade from 9.0.1 to 9.1.1; this introduces a startup error, see the image attached.
The error shows when clicking play from the launcher.

CRITICAL ERROR: VERSIONING! RemoveUnderwater
Main.Main.Water

I tried searching and even removed the underwater shader files, but this did not change the problem.
I uninstalled OR; game starts fine then. Reinstalled OR and the error is back.

Any ideas?

Did you uninstall all old files before installing new files? You should always uninstall all old versions completely before installing a new version.

I uninstalled the plugin and files through Wrye Bash and checked if the folders were gone. They were.

That answers that. Are you running ReShade or ENB?

No ENB. Reshade is something similar, right? I installed everyting a few months ago but I think I stayed away from ReShade as well. With OR 9.0.1 the game was running.