Recent iOS updates may cause iPhone Mobile Authenticators to reset, preventing account access. When you update your phone's OS, we recommend taking any one of the following precautionary steps:
•
Sign up for the free SMS Protect service. In the event of a lost, broken, or accidentally reset authenticator, users with SMS Protect can remove the old authenticator from their account with a texted security code. For more information,
visit the SMS Protect FAQ.
• Update over Wi-Fi. We have received reports that iPhones that are updated over Wi-Fi, rather than through a computer, are less prone to accidental resets.
• Write down your authenticator's Serial Number and Restore Code so that you may
restore your authenticator to your phone after the OS update is finished.
•
Temporarily remove the authenticator before updating. Reattach the authenticator again once your iOS update is complete.
Source.
^Unsure if anyone saw this or what have you but it's useful nonetheless.