Since yesterday, I am seeing the first one consistently. The message 'An internal error occurred while this artifact was being saved' is showing up in the logs.

Yeah, last Friday I could get some green builds, but then got to the same issue you are facing, "pending requests" forever...

The builds are running again!

One branch it is working, other is failing on: "Export archive for development, ad-hoc & app-store distribution". The weird part is that the branch that is working was recently rebased on the one failing.

I followed this other documentation: https://developer.apple.com/documentation/enterpriseprogramapi/generating-tokens-for-api-requests and generated a JWT token manually. With it, I could curl -v -H 'Authorization: Bearer ' "https://api.enterprise.developer.apple.com/v1/certificates" with success, but for https://appstoreconnect.apple.com/notary/v2/submissions? it fails with 401. Failed for both keys, Developer and Admin access. I also tried changing "aud": from apple-developer-enterprise-v1 to appstoreconnect-v1, just for the sake of trying.