Generally the firmware update is successful during the out of box setup, and if you've confirmed it previously I'd recommend avoiding using too often - flashing and reflashing firmware is necessarily something you want to do for fun
As for this issue, I raised with the dev team this morning, and we're looking into it. If you guys can provide me with any and all information that might be pertinent, it would be very helpful - ie conditions when it happens, doesn't happen, etc.
For now, a hard reset (NOT FACTORY RESET) is the workaround - hold the power button down for 10s, then release. Then power on as normal.
Thanks!
James