Mature project doesn't sign artifacts on release when run from new Mac

I have a mature Gradle project from which I’ve published many releases from a previous developer machine (Windows 7). I recently migrated to a new machine (MacBook Pro), and my artifacts are not getting signed when I execute the gradle release command. When I run with debug output enabled, I see messages about the signing tasks being “realized”, but the ASC files for don’t get generated for any of the artifacts except for the POM file. Consequently, I can’t publish my release.

I can generate the ASC files by running the signing tasks manually, so it seems that my GPG configuration is correct. Can anyone suggest what I should check to enable publication of releases from my new machine?

The project can be found here