The powering down of the Nomad and removing the USB cable causes a full reset of the interface board - a computer really - in the Nomad. Most likely, that it what "fixed" the issue. Powering off the Nomad and not removing the USB cable does not cause the reset.
If the problem repeats, keep track of the incidents. If they become more frequent or restoring become more difficult, look into the methods @WillAdams pointed out. If you're up to taking your machine apart and doing some simple solder work, adding a capacitor has dramatically reduced USB issues for many.