I've been having problems with this lately, every few days it drops to about half the IPs blocked and slowly builds up to 2.5 billion blocked (what it should have) and then drops down again. Something must have changed that interferes with his algorithm.
Usually I get thousands of blocks with this list every session but when it drops down I only get hundreds. There is more info and different blocklist discussion here https://gist.github.com/johntyree/3331662
but this code really needs to be fixed. I recommend once you see it blocking around 2.4-2.5 billion addresses you stop it from updating for now.