I completely understand. I was thinking of it as more of a gift without any binding requirements, but I could see how it could give you a lot of stress.
Thank you so much for putting in all the hours and take a break if you can. I worked as a dev until a year ago too so I know how that desire to get to the bottom of a bug can keep you up till morning. Of course I trust your ability since I'm pretty sure it's nowhere near as complicated as The Medium plus there was a patch for Nioh 1 which uses the same engine.
On that note, there's already a patch out like you said and it works reasonably well (fork of Nioh 1 patch): https://github.com/Filoppi/Nioh2Resolution