OAuth2 issues after upgrading firebase

I have a working android app (Maybe better say HAD).

The app is using some third party libraries including: Google maps, Firebase, firebaseui. After converting the app to use the new firebase I have stumbled upon two main issues:

1. The firebaseui logon screen changed and now looks like this: which is of course completely different from the old one and for some odd reason different from the debug build variant.

2. I am unable to use the google sign in with the following error showing in logcat:

com.google.firebase.FirebaseException: An internal error has occured. [ OAuth2 client id in server configuration is not found. ]

Again this issue is not happening in the debug variant.

Just to be clear the debug build variant uses the same code base but a different firebase database.