Hey sorry for the super late response on this. I think I have a fix: Can you try downloading this version of the game from this link?:
https://abhimonk.itch.io/spectral-slash-lighting-fix?secret=3xLTIItqjm77Vi3Lf0uvClb0BY
I made some changes to the lighting shader that I think will hopefully fix the issue for you. If you have the time, can you give it a try and let me know if it works?