Perhaps this is relevant, then. We are displaying comment numbers on articles and on the home page (so that might entail a LOT of API calls), and I’ve noticed in a few cases where the comment number is correct but fewer posts appear below the article. That’s still true here for instance, where the comment number is correctly reported as 4 but only two posts show:
Unfortunately, I haven’t been able to identify any pattern with when it has worked and when it hasn’t. We’ve been using CloudFlare the entire time, and most settings have been quite static during this time (we brought the site online in April 2018). I recently turned off CloudFlare’s Auto Minify JavaScript and Brotli compression to work around posts not refreshing quickly after editing, but I can’t see how that would be related. And I think the problem predates that change anyway.