firebase_auth/missing-client-identifier error starting to be thrown to a limited number of users recently

Question

We are using Firebase auth on a React Native app using react-native-firebase for several years now (currently at 12.9.3). A few days ago, without a new Android release or changes in the Firebase console, an Android user could login in the morning but then could not any longer in the afternoon and then after and getting this "firebase_auth/missing-client-identifier" error message.

I have searched here and at the react-native-firebase issues at GitHub but could not find any cases that this happens to only one user. Then yesterday, a second user started facing the same problem which is worrisome.

I checked the SHA-1 and SHA-256 fingerprints and everything is setup correctly and that is why thousands of other users are not facing an issue.

Any ideas of what could be causing this?

Thanks!