My mistake about the resourcepack - datapack thing!
I think something has happened between 1.16 and 1.17 that has made some of the old code in the pack broken, because whenever a spider is spawned, its texture is completely broken (see attached picture). Just figured it out though, I had forgotten to delete a lot of spider related jpm files under assets/minecraft/optifine/cem. Deleted them all and it worked, but doesn't fix the spiders rather than just exempting them from the pack altogether. I even tried to then add back in the old textures, but it was still broken (see second picture).
