Luke Le on 22 Jan, 2018 12:21 PM
this is an issue we have seen with some users, and have since been able to understand what is happening but not exactly why. Did you use your key on different computers? One cause is, that a user created a new sub key on one computer, but never exported that new sub key to their other computers. After talking to the developer of GnuPG we believe that GnuPG 2.0.X handled this behavior differently than GnuPG 2.2.X, which might also explain why a downgrade to GnuPG 2.0.X (included in 2017.1b3-v2) solves the issue.
@Luke just a heads-up that I tried this downgrade process from 2018.1 to 2017.1b3-v2 on a High Sierra laptop earlier today, and I found that it overwrote my keychain without a confirmation or warning, which seems pretty dangerous.