It's difficult to know what to suggest for this since we've never seen this sort of behavior before in the office. One thing that you could try would be another USB cable. We had a user earlier this week who had some trouble b/c he was using a very long USB cable. I don't know the length of the cable you're using, but it would be good to try another.
Also, you've tried a system restore. It might help to reinitialize the PitchFactor to its system settings restoring its factory presets. If you have presets on your PitchFactor you don't want to lose, you could back them up with FactorLib or H9 Control if you can get through that without being interrupted by a Communication Error. To reinitialize your PitchFactor to its factory state, power it off and then on again while pressing the algorithm selector knob and the middle footswitch.
Let us know if the problem persists. I guess the next thing to check would be whether you see the same behavior on another computer. We don't usually have trouble with users on Macs, and it would be surprising though if it were something specific to your computer rather than your PitchFactor.