If I click the '[n] new posts! click here to view them' message on the... home page? timeline? chostfeed?... a series of new posts are displayed and everything seems fine, but if I then refresh the feed using the browser's page-refresh button or by clicking the cohost logo, sometimes more posts appear interspersed among the ones already revealed by clicking the '[n] new posts' message. The time-stamps indicate that the previously unseen posts are in their correct chronological places, it's just that they weren't visible before. So the '[n] new posts' button seems to be causing only some new posts to load, not all of them.
This tends to happen most when the number of new posts is quite high. When the number is in single digits, all of them seem to load. As far as I can tell there's no pattern to which posts are omitted. It certainly isn't whole accounts being left out: sometimes some posts from an account will be displayed but others not.
So far the only browser I've tested this on is Brave (which is not great, I know, I keep meaning to change but inertia) and the only computer I've tested it on is a 2019 MacBook. I've tried lowering all 'shields' (switching off all Brave's built-in blockers &c.) for cohost.org and it doesn't seem to have made a difference.
This is not a big problem because the simple work-around is just to refresh the page rather than clicking the '[n] new posts' message, but if other people are having the same problem they may not be aware that they're missing out on some posts.
Couple of additional bits of information: