You can only review 20 close votes per day.
Yet I've reviewed 90 posts this week, while the maximum should have been 3•20=60. Similiarly, I've reviewed 162 posts this month, while the maximum should have been 4•20=80. In fact, the only day in this month, but not in this week, was August 1. It looks like I have reviewed 72 close votes on that day.
Looking into my review history, I actually never crossed the threshold. It is just that the stats are off. It happens at all users.
This is happening to all users on Math.SE, and also in all queues. I can't access enough data on other sites to decide whether it happens there as well.