Yep, I since discovered the same thing. The account owner (not me) was able to create Developer ID certs, but there’s still a problem - because she requested the cert (using Keychain Access), when I download the cert, there’s no associated private key, so signing still fails, but now with a slightly different error message.

We don’t know how to resolve this. I’ve asked Apple support, seems they may have broken something, or else we just don’t understand how it’s supposed to work (quite likely). Waiting on their response.

—Graham