iOS mobile device stops syncing after recurring MFA authentication failures (every 60 days)

A user is experiencing a recurring authentication and sync issue on an Apple mobile device.

Approximately every 60 or so days, the user is prompted to re-authenticate using a verification code (his MFA app has also already been set up successfully before). During this process, the user is asked for the verification code around three times. Today the laptop displayed “authentication failed”. Despite this, access to the account was granted.

After this occurs, the user’s mobile device no longer syncs correctly. Reported issues include:

• Calendar updates failing
• Meeting changes not syncing

What steps are recommended to permanently resolve this issue and prevent it from recurring?