Unfortunately I don’t have exact steps to reproduce - entirely random when it comes up. Have had a few users come up and say they’ve had topics they just posted in show up in their unread/notifications. Various browsers, no obvious firewall rules or plugins - one member going so far as to use a stock install for a while just to test.
Up to date chrome install >v100 (that I can test) and it’s totally random whenever a reply will result in going back to the category view and seeing Topic name(1) last post by: selfUserName.
I even had it happen here on meta with my Backup Schedules post. Unfortunately I didn’t screenshot in time. I clicked into the topic quickly thinking someone had replied to me very quickly, but it was in fact my reply.