Essentially the UBlocker is a computer, so "why computers freeze?" there is no single answer -- it could be some hardware or software issue, or it can also be related to some issue external to the device such as the router or wifi software.  If your Ublocker is no logging calls in the 'call log', power cycle your Ublocker.  Just wait 2-3 minutes before powering back ON again.  This should fix the problem 99% of the time.  

If after powering OFF and ON your UBlocker it's still not logging calls online, please contact our technical support.