As far as I can tell, the numbers that show up in the page title are entirely random. For me, our local community forum has been stuck on ‘12’ for at least a day and a half now:
And when I say “stuck on” what I mean is that I see there are 12 new things to look at (there aren’t) so I go to the tab, and read or dismiss the two, or four, or… seven things that have changed since the last time I was here, and then go back to other things. When I look up… 30? 45min later, the number is at 12 again. But it’s not always 12. Being stuck on a number is a new thing. Usually it’s some random small integer that is almost always higher than the number of New threads, Unread posts, or Notifications - very often combined.
This has been going on for quite a while, but it took me a while to first register the behavior and then do a good capture.