Can't disarm with keypad after power failure

I recently experienced a lengthy power failure that knocked out the wifi router. When a family member entered the house to check on it, the entry delay was triggered, but she could not disarm the unit using the keypad. I received a call from Ring and told them it was a false alarm. I had to deregister the system on my phone app to stop the alarm. I'm puzzled. How did the system have enough battery and functionality to sense that the door was open, start the entry delay, and notify Ring of a "burglary attempt" -- but not enough to permit disarming using the keypad (or, for that matter, using the phone app, until I deregistered)? Seems like a Catch-22 situation.