Firestore keepalive

FirebaseHeartbeatConnector.java

private FirebaseDatabase firebaseDatabase;

private DatabaseReference connectedRef;
private ValueEventListener connectionStateListener;

public FirebaseHeartbeatConnector(FirebaseApp firebaseApp) {
    L.i("FirebaseHeartbeatConnector() called with: firebaseApp = [" + firebaseApp + "]");
    firebaseDatabase = FirebaseDatabase.getInstance(firebaseApp);
    firebaseDatabase.setLogLevel(Logger.Level.DEBUG);
}

private void doSendFirebaseHeartbeatRequest() {
    L.i("doSendFirebaseHeartbeatRequest() called");
    connectedRef = firebaseDatabase.getReference();
    connectedRef.keepSynced(true);
    connectionStateListener = connectedRef.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot snapshot) {
            Boolean connected = snapshot.getValue(Boolean.class);

            if (connected == null) {
                changeState(FirebaseConnectionState.error);
                return;
            }

            if (connected) {
                changeState(FirebaseConnectionState.connected);
            } else {
                changeState(FirebaseConnectionState.not_connected);
            }
        }

        @Override
        public void onCancelled(@NonNull DatabaseError error) {
            L.i("FirebaseConnectionStateListener was cancelled");
        }
    });
}

I tested this with the below code and it didn't timeout after 60 seconds for me.

FirebaseDatabase.getInstance().getReference().keepSynced(true);
DatabaseReference connectedRef = FirebaseDatabase.getInstance().getReference(".info/connected");
connectedRef.addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(@NonNull DataSnapshot snapshot) {
        Boolean connected = snapshot.getValue(Boolean.class);

        if (connected == null) return;

        if (connected) Log.d("presence", "connected");
        else Log.d("presence", "disconnected");
    }

    @Override
    public void onCancelled(@NonNull DatabaseError error) {  }
});

That' really strange. I copy/pasted your code and it worked once. Then I added my firebaseapp-instance as paramter for FirebaseDatabase.getInstance() and it didn't work anymore (1 minute timeout). Then I removed the firebaseapp-instance and it also didn't work anymore...
Then I completely uninstalled the app and went back to your code again => does not work anymore....
i have no idea what's going on there and unfortunately I have no time left to play around with it. So I will implement a normal online-check using the CONNECTIVITY_SERVICE.
Thank you for your time and effort trying to figure this out!! I hope the documentation will improve on this topic.