No matter what I click I can't see the flagged post. But maybe I simply don't know something. Or maybe it's my browser, my firewall, my proxy etc. So what should I see?
Yep, that's what the page looks like when there are no flags available to review.
It just so happens that the only flag currently in the review queue is one you flagged, so it doesn't make sense to show it to you again as you can't action it (excuse my publicly divulging that info, but I can't see it being a problem).
Why you see the
(1) notification for flags, I'm not sure. I seem to remember the same thing happening for me before I got to 10k, and I'm sure I've seen questions about it on the main meta site before. But I can't find anything right now.
99 times out of 100 things like this can be blamed on cache.