I've updated to windows 10 technical preview.and tried to roll back to 8.1 using the windows phone recovery tool. But it wont work. Since update cant install music update one drive update and
Windows Phone recovery tool has nothing to do with the update of apps on your phone. It actually wipes your phone completely and install the OS available for your phone.
The issue might be due to the following
1) A bad USB port (On the phone or the computer)
2) A bad USB cable
Try changing cable or changing USB port on the computer.
Posted on Lumia 1520 via Taptalk