Weirdly, it had already been in a folder with all permissions, but removing those permissions and then re-adding them fixed it! This is extra-weird because at one point I completely replaced my fresh itch.io install with one transferred via USB from a friend's computer. Both versions had the same issue, even though neither versions of the files had been denied rwx at any point. Hopefully this helps pinpoint whatever might have caused this issue to keep it from cropping up in future releases.