Preferences values are not saved - libgdx

Newbie & Debugging Questions
#1

I would like to save the player’s best score+2 other values in the game’s preferences file. Now, I know I need to call the flush() method in order for the values to get persisted, but from some reason they are not saved at all.

For instance, let’s say I turn off the music in the game. When I exit the app and then start it, the music is on.

I call the flush method in my preferences object but it still doesn’t save the value into the preferences file.

Here is my settings class:

public final class Settings {
    private boolean soundOn;
    private boolean musicOn;
    private int bestScore;
    private static Settings instance = new Settings();

    public static Settings getInstance() {
        return instance;
    }

    private Settings() {
        soundOn = ScreenHandler.getInstance().getGame().getPreferences().getBoolean(Values.KEY_SOUND, true);
        musicOn = ScreenHandler.getInstance().getGame().getPreferences().getBoolean(Values.KEY_MUSIC, true);
        bestScore = ScreenHandler.getInstance().getGame().getPreferences().getInteger(Values.BEST_SCORE, 0);
    }
    
    public void setSoundOn(boolean soundOn) {
        this.soundOn = soundOn;
        ScreenHandler.getInstance().getGame().getPreferences().putBoolean(Values.KEY_SOUND, soundOn);
    }

    public void setMusicOn(boolean musicOn) {
        this.musicOn = musicOn;
        ScreenHandler.getInstance().getGame().getPreferences().putBoolean(Values.KEY_MUSIC, musicOn);
    }

    public void setBestScore(int bestScore) {
    	this.bestScore = bestScore;
    	ScreenHandler.getInstance().getGame().getPreferences().putInteger(Values.BEST_SCORE, bestScore);
    }
    public void save() {
    	ScreenHandler.getInstance().getGame().getPreferences().flush();
    }
    public boolean isSoundOn() {
        return soundOn;
    }

    public boolean isMusicOn() {
        return musicOn;
    }
    
    public int getBestScore() {
    	return bestScore;
    }
}

Whenever I set the values in the game, I call the save method which invokes the flush method in the preferences object.