I had the same issue some weeks ago. Doing a CTRL + F5 (Instead of only F5, in order to force a complete reload of the page, ignoring cache) solved the problem. (on Chrome)
I’ve been testing this for a few days. I cleared the cache on my browser but the notification repeated every day. I then tried using a different browser to access the BA site for a couple of days, and the same situation occurred, so I don’t think it’s a browser issue.
There is only one post that triggers this problem - the post that I linked in my question above - and it occurs once per day. I clear the notification, and it’s gone for the day, but the next day it is back again.
My (admittedly naive) guess is that there’s something messed up with the BA site’s activity record for that one post. Somehow it keeps getting reset to ‘unread’ every day.
I had the same issue with a reply notification. I unsubscribed from the topic and it went away. I don’t think it was a browser issue as the notifications popped up on my phone as well. I’m sorry to say I don’t remember what topic or reply it was.
But at least I can corroborate that such a thing might happen.