Warum zeigt mein FirebaseListAdapter keine einzelnen Elemente in Firebase-UI 3.1 an?

FirebaseListOptions<ChatMessage> options = new FirebaseListOptions.Builder<ChatMessage>()
        .setQuery(FirebaseDatabase.getInstance().getReference("Lobbies").child(leaderID).child("Messages"), ChatMessage.class).setLayout(R.layout.message).build();

adapter = new FirebaseListAdapter<ChatMessage>(options) {
    @Override
    protected void populateView(View v, ChatMessage model, int position) {
        // Get references to the views of message.xml
        TextView messageText = v.findViewById(R.id.message_text);
        TextView messageUser = v.findViewById(R.id.message_user);
        TextView messageTime = v.findViewById(R.id.message_time);

        // Set their text
        messageText.setText(model.getMessageText());
        messageUser.setText(model.getMessageUser());

        // Format the date before showing it
        messageTime.setText(DateFormat.format("dd-MM-yyyy (HH:mm:ss)",
                model.getMessageTime()));
    }
};

@Override
protected void onStart() {
    super.onStart();
    adapter.startListening();
}


@Override
protected void onStop() {
    super.onStop();
    adapter.stopListening();
}