We've resolved this by permitting TLS 1.2 traffic as well as TLS 1.3.

Can anyone comment on this HTTP 500 error? To reiterate, I've been blocked for a week now on submitting an app update due to this issue and another, which both appear to be regressions of standard Xcode Cloud functionality. (https://developer.apple.com/forums/thread/819249).

Filed here: FB22276321 (Xcode Cloud build encountering persistent Connection Refused error)