Surprisingly, I just tried again, and this time it worked. I haven't changed anything in my configuration, not even rebooted. One thing weird is that Xcode did take a while to start as if newly installed, but I checked on the MAS app and Xcode doesn't seem to have been re-updated since last time.

Thanks, here's the FB number : FB13449783.

Seems to be a cache/setup issue, as the 'clang-1500.3.9.4' indicates. I can't delete this post but please ignore it.

Thanks. We know the account has no pending agreements and that Xcode is logged into it, as there are other projects being built by the same CI machine using the one same account, but not using xcode managed signing. I'll try a Clean Build.

As I said, all the apps have their signing managed by Xcode, so they have a provisioning profile. Also, I've done a build+TestFlight release for each of them "manually" from my own machine, and building an archive for any of the apps also works using Xcode manually on the CI machine. It's really just 'xcodebuild archive' which fails in this manner.

I couldn't find such an entitlement here https://developer.apple.com/documentation/bundleresources/entitlements but the entitlements are the same ones as other apps which are presently distributed on the App Store so I doubt that's the problem. I'll contact the Support team, I'm really at a loss as to what the issue could be.

So I understood :-). Instead I just reset the setting a to a normal value : defaults write com.apple.dt.Xcode DVTDeveloperAccountManagerAppleIDLists -dict 'IDE.Identifiers.Prod' '({ "identifier" = "DEADBEEF-8599-416C-8362-E12AE4D7424F"; } )' "IDE.Prod" '({ "username" = "<apple_id>"; } )'