Had this replacement device for 1-week (faulty power lead on previous version) & it occasionally loses all WiFi connections.  Looking through the list of available WiFi nodes (of which there's normally 5 or 6 available), all are suddenly not available.  A complete reset (holding power button for 5-sec & then re-starting) seems to clear the problem.  Is this a hardware or software problem - should I exchange it for another replacement?