Expired Refresh Token
In a perfect world, this should probably not happen. Token Refresh Jobs are scheduled to execute every 7 days and — if they always execute according to schedule — the refresh tokens will not expire. However, things tend to happen in the real world. If a server is down or some other issue occurs that prevents the token from refreshing, it will exceed the 15 days since it was created and expire.
For any expired token — regardless of cause — the remedy is the same. Look for any that show as Expired and execute the Reactivate Token Refresh Job function (see preceding sections).