Hi Mark,
the one thing that I could think of that you didn’t already try, is to move the device to a different USB port. Or to connect it directly without a USB extension cord. The power consumption of the REX is close to what the USB specs allow, and some USB ports just won’t work. We have also noted issues with some USB extension cords, probably for the same reason.
If this still doesn’t help, please contact our technical support staff. You can use the contact form here.