Oh, yikes, this isn’t cool at all. I have a suspicion that the caching process is behind the madness here, but I’m going to dig into it and get back with you soon.
(Slightly) more info: Some active posts are being skipped. I currently have Landing Page Post Count set to 4, and I’m seeing only two on the landing page. The two missing posts were published in between the two that are showing. Weird.