Thank you very much for your confidence in my extensions.
If shared sessions are enabled in Joomla settings this drop-down is disabled as you would be always banned if you enable the 'user session protection' in Securitycheck Pro. Shared sessions in Joomla allow you to automatically login in frontend and backend and the 'user session protection' protection feature of Securitycheck Pro forbids that.
If do you want to enable 'user session protection' in Securitycheck Pro just go to Global configuration --> System --> Sessions settings and disable shared sessions in Joomla settings. After that click on the wrench icon and enable this option in Securitycheck Pro.