Hi! Sorry it took a while. I haven't found the problem yet but I did update the 1.16.5 version to the new 7.6. Maybe it'll work now?

https://modrinth.com/mod/simply-no-shading/version/7.6.1+mc1.16.5

I'll close this for now. Feel free to reopen or create a new issue when it happens again. Also, try adding more details next time, it'll make it clear what exactly is not working (e.g. this one and that other thing is broken. or everything was broken).