This topic seems to be stuck. Whenever I read it, it just keeps coming back. If there are other topics in unread this one appears below a divider line labelled “viewed today” or something.
I’ve notice that Discourse has had a hard time recently figuring out what I have read after I have looked at a thread for a while. For the ones that are stuck as unread, at the bottom of the thread, change it from Tracking to Normal.