Just happened again. Checking the cgminer logs this is the error I get:
[2014-01-28 20:53:32] HFA 0: Bad work sequence tail
[2014-01-28 20:53:33] HFA 0 HFClearRead usb read err:(-9) LIBUSB_ERROR_PIPE
[2014-01-28 20:53:33] HFA 0 attempted reset got err:(-5) LIBUSB_ERROR_NOT_FOUND
[2014-01-28 20:53:38] Hotplug: Hashfast added HFA 1
In most cases I end up with two devices HFA 0 reporting some crazy TH figures, and a new HFA 1 device working correctly. In some cases HFA 1 does not appear and mining stops.
On BFL devices these types of things are usually due to USB cables or hubs that are bad. Dunno about hashfast as I don't have mine yet.
