According to the review bar there should be a number of posts that require review, but that does not seem to be the case.
When I click on 7 then an overview of posts is shown, but none of them require a review as everything is 0
The top bar is dead! Long live the new top bar!
The new top bar only lights up—it no longer has a counter.
The number indicates the total number of review tasks waiting in the system, regardless of whether you've reviewed them personally or are eligible to review them.
At least some of the review tasks are actually your own suggested edits, which you're not eligible to review for obvious reasons. There are probably other reasons why you can't see the other tasks — perhaps you've already reviewed them, and they're still waiting for other users to review too.
Fortunately, the issue of incorrect counts will be gone (or at least different) when the new top bar rolls out shortly. At that point, the review icon will simply light up if there are a sufficient number of review tasks (although the underlying logic still won't check if they're tasks that you are able to review personally, so it's not really fixed... more hidden).
See also: What does the number next to the review link in the top bar actually mean?