I use two factor auth but not this app, so I am not sure why people are going to have such a bad day...
The app is "forgetting" and no longer displaying the accounts you add, such that you open Authenticator and it's empty.
You can no longer log in to your Google account without one of the 10 printed one-time access codes you made when you first set it up.
* or a backup phone number that's been verified (i.e. send a verification code and confirmed).
Edit: tweet with picture: https://twitter.com/jawj/status/375144792126410752