Lastly, it seems the false "expired" issue is not limited to just the dashboard message. When I go to App Store Connect > Xcode Cloud, it says "Apple Developer Program membership has expired; To continue using Xcode Cloud, renew the program membership." I'm guessing there may even be further limitations caused by this false positive "expired" detection.

Just encountered the login issue again where it wouldn't recognize my password, which occurred on Safari but not Chrome on my MacBook, this time at https://developer.apple.com/account which redirects to https://idmsa.apple.com/IDMSWebAuth/signin?appIdKey=... I also notice I can't update my contact details at Apple Developer dashboard > Update your information. It goes to an error at https://developer.apple.com/unauthorized/: "Your account can’t access this page."