When the most recent poster in a thread happens to be on my ignore list, Discourse won’t mark the thread as completely read for me. I always scroll well past the point I see the ignored poster placeholder, but that thread will show as still having new posts until someone else posts and then I can read past that one.
It does that sometimes. Seems not to do it as often to me of late. Only advice I can think of is to turn off your browser extensions and see if it still does it. If not, it’s one of them. If so, it’s just Discourse.
I’ve found that if I just ignore that thread and don’t open it, after a few days it stops showing up in the “Suggested topics” list.
This still happens to me. It’s definitely Discourse, not my browser extensions. It happens in all the different kinds of lists of threads Discourse can generate for me, not just the suggested list at the bottom of threads. C’mon, Discourse, if I’ve paged past that point, just mark the damn thing as read so you don’t keep lying to me and telling me there’s an unread post worth reading there. I ignore idjits for a reason.