Blocked count fluctuates heavily

Installed FV Antispam plugin and it works great.

Just one problem. The “Blocked” comments count on the Dashboard shows wildly fluctuating figures. One day it’s in thousands, next day it’s in hundreds, third day in double digits, and so on. But actual number of comments blocked are nowhere near these numbers. What could be the reason?

https://www.ads-software.com/extend/plugins/fv-antispam/