After trying with both the release and beta version of Xcode and still getting the error I tried one of my older archives that have previously uploaded without error.
I expected the error to be about this build already having been uploaded, but instead it was this invalid code signing error for app-groups on my 3 bundled app extensions.
This makes me think it is a server-side issue.
Topic:
Code Signing
SubTopic:
Entitlements
Tags: