Same issue and it just started today. I was able to successfully upload an archive yesterday by building in Xcode 11 and uploading using 12.2 but today every combination I've tried fails as well.
ggoodwin
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I believe the issue has to do with renaming the application package for Xcode. I'm needing to run Xcode 11 and 12 beta. I moved Xcode 12 beta into my applications directory and renamed it to avoid overwriting Xcode 11. After moving Xcode 12 beta back to downloads and renaming it back to "Xcode" all works again.