I've had a similar issue on a rare occasion. It seems to happen when I am attempting to top off a charge (starting at 80% or above) or when I mix up the sequence of connecting the bike to the charger and the charger into the outlet. The fix is as you described, simply remove the battery and reinstall. I follow another posters advice and ALWAYS keep a battery key with me when riding the bike. My recharge process, which is probably bassackwards but seems to work well, is to do as follows.
1. Turn off bike
2. Plug charger into the bike
3. Plug charger into the outlet - charger shows one orange and one green light
4. Wait a few seconds
5. Turn bike on
6. Place bike in lock mode
Once charged - charger shows two steady green lights
1. Unplug from outlet
2. Unplug bike
3. CLOSE charging port on bike
The N/A happens fairly rare, and when it does the fix is quick and easy. I just figure there is something a little dodgy between the charger>battery>controller code that will some day be ironed out in a firmware update.
Which BTW has anyone seen a sign of the alluded to forthcoming firmware update?