The count in the top bar is site-wide, and includes [items which you may have already reviewed or skipped][1], both of which no longer appear for you in the individual queue counts.

There's also caching, but that only lasts a minute or so.

To see the full counts, visit [/review][2] while logged out (e.g. in an incognito window).


  [1]: https://meta.stackexchange.com/q/233535/189912
  [2]: https://serverfault.com/review