I checked my servers today and i found no IP address gets blocked by SSHblock even though i think there were some IP addresses that should have been blocked.
After taking a closer look on the configuration files, i finally spotted the problem. It seems that i put a wrong log file to watch in the rc.sshblock script. I change it to the correct log file (/var/log/messages) and it finally works as intended.
I have re-submitted the SlackBuild package to SBo and also pushed the single change to my SlackHacks repository. I didn't bump the BUILD variable, so you just need to adjust the path according to this git commit and it will work.