I have two tablets with identical specs and they are both exhibiting the same problem.

Symptom: I plug in a USB device. After a few seconds, the device is recognized and all is well. However, after some time [minutes?], the power to the device is gone and the device is no longer working. This occurs in the USB A port, so I tried using a powered hub in the USB C port, but the results are the same. After a while, the power drops out and the device stops working. It's as if I had unplugged the device. If I do unplug the device, and reinsert it, I can eventually get it to work, but only for a short period. 

I've done an SFC scan and all is well, I've uninstalled the hub and the device, and I have the latest drivers and Bios installed. Any ideas?

Thanks in advance.