The review queue presents itself across the top like:
Which when you click on it takes you to:
The numbers almost always are out of sync with what is in the queue, (the pictures above show 7 whilst all the different categories are empty - i.e. a real time scenario).
1/2 hour previously it read 4, then bumped up to 9 (but there were 7 new things in the queue - so it should have gone to 11) I deal with those and then came back to see a 7 displayed (implying that I'd only dealt with 2 - when it should have shown 0) and now it has been stuck at 7 for about 20 minutes.
I understand a processing delay, or a lower priority (background) process so I don't expect this to be an absolute status indicator, given how dynamic this site can be, but this seems to me more like sticky behaviour i.e. a bug.