How to fix:
Go to Build -> Actions -> Archive - iOS -> Artifacts
Download "Logs for archive"
unzip the file and look for "<app name" Build 63 Logs for /xcodebuild-archive.log"
Look for string "error:" and the exception should be noted there
For me, it was due to a missing file.
Topic:
Developer Tools & Services
SubTopic:
Xcode Cloud
Tags: