I updated the build project for this blog recently, as the engine used to generate it was updated. But doing that caused an issue which I think others might bump into. So here's an explanation of what I saw and how to fix it:
I hit a rather confusing issue with a release a while back, which initially appeared to be a Unicorn problem. But after investigating the details, I think this was actually an infrastructure problem causing some odd behaviour. I doubt this is a common problem, but still worth writing down in case it's a challenge for anyone else...