i had the same issue with my own site on github. www redirect caused a 301 redirect and broke cors for me as well. turning off the automatic www redirect seems to have fixed it right away
thanks for finding the fix!
Discussion
One big happy CORS-issue-free family 😆 You got it, thanks for confirming I’m not insane, started questioning my terminal lollllll
i've never used github for hosting. i see a lot of people doing that now. maybe ill do that with a random domain to play around with an application at some point when i have more time.