Unable to Update UI using LiveData and Room

I am writing and reading to a local SQLite database using Room and LiveData. I have successfully read and wrote to the database, as I am using Stetho to confirm.

I understand LiveData handles functionality on a separate thread. I am struggling with updating my RecyclerView based on the database information I retrieve using LiveData:

    private void retrieveTasks() {
    final LiveData<List<Movie>> movies = mDb.movieDao().loadAllMovies();
    movies.observe(this, new Observer<List<Movie>>() {
        @Override
        public void onChanged(@Nullable List<Movie> movies) {
            for (Movie movie : movies) {
                String photoURL = "http://image.tmdb.org/t/p/w185" + movie.getPoster_path();
                Log.v("FAVORITE_URL", photoURL);
                mMovieURLS.add(photoURL);
            }
            runOnUiThread(new Runnable() {
                @Override
                public void run() {
                    mMovieResultsAdapter.swapDataSet(mMovieURLS);
                    mMovieResultsAdapter.notifyDataSetChanged();
                }
            });

        }
    });
}