Android FirebaseMessaging - getToken fails for some users

I have the following setup in my grade files:

project:

        classpath 'com.google.gms:google-services:4.3.10'
        classpath 'com.google.firebase:firebase-crashlytics-gradle:2.8.1'

app:

    implementation platform('com.google.firebase:firebase-bom:29.0.0')

    // When using the BoM, you don't specify versions in Firebase library dependencies
    implementation 'com.google.firebase:firebase-crashlytics'
    implementation 'com.google.firebase:firebase-analytics'
    implementation 'com.google.firebase:firebase-messaging'

After the users logs in, I'm doing

FirebaseMessaging.getInstance().getToken().addOnCompleteListener(task -> {
    String refreshToken = task.getResult();
    ....
}

which is fine for most users, but for some (not only a few) get errors like FIS_AUTH_ERROR, MISSING_INSTANCEID_SERVICE, SERVICE_NOT_AVAILABLE.

I guess (!), MISSING_INSTANCEID_SERVICE is no Google API on the device, SERVICE_NOT_AVAILABLE missing network (?) but I'm not sure at all. And I have absolutely no clue about the FIS_AUTH_ERROR. Is there some documentation about this?

from Android FirebaseMessaging - getToken fails for some users