1) Retry Update after restarting Air unit. Do this 3-4 times.
2) See the error code in admin panel for OTA. If status=9 and state = 0,1 or 4 and already retried 3-4 times then the issue is related to hardware.
3) Retrying OTA from mobile app 3 times or more will disable the OTA screen on mobile app and user will be able to use the older version again.