Default XZU stop recognising USB is plugged in.

Over the past few days I've had an issue where my XZU seems to stop recognising it's plugged in to a USB port. It will work fine then it stops charging and I can't see a device on Windows anymore. In other words it's as if it isn't plugged in anymore. Charging from AC still works normally.

I've tried unplugging the cable, swapping USB ports, rebooting XZU. The device won't mount as a mass storage device in CWM. Rebooting Windows is the only thing I've tried that fixes the issue but it happens again. So I gather it could be a Windows issue although I haven't changed anything on my Windows installation that I recall. I have however been flashing various firmwares onto my phone. ATM I'm using stock firmware and I *think* the issue has only happened with the stock firmware.

Edit: Now it's still happening when I reboot Windows :|

Can anyone suggest anything to try to fix this annoying problem?
Sony Xperia Z Ultra LTE 6833 / Stock .757 / DooMKernel v16