Unknown random users in Firebase authentication.

I recently noticed that random users have been appearing in my Firebase Authentication. They seem to be autogenerated Gmail accounts. Is this normal, or should I be concerned? My authentication methods include Google, Apple, and regular email/password.

My app is still in development and is only available for internal testing on Play Console and TestFlight, with access limited to myself.

Additionally, these random accounts don't have a corresponding users collection in the Firestore database (there are no users with their given User UID in the database), so they didn’t sign up through the app. Could this be just an authentication issue?

Thanks in advance for your help!