Just to update everyone - we managed to replicate this bug in testing today. It is incredibly rare - it seems to happen less than 1% of the time.
We will obviously be working on a fix. But for now, anyone affected should factory reset using the button on the back.
To do this, make sure the router is powered on. Then take a small object like a paperclip or a pen and push down on the little reset button. Wait for the lights to blink off and then on again. Wait about 30 seconds to 1 minut