Can't see any Camera, Viewscreen and Stage in your GameScreen. If you got some, don't forget to add Board actor to the stage. I have mine in Main class:

    @Override
    public void create() {
        guiCamera = new OrthographicCamera(SCREEN_WIDTH, SCREEN_HEIGHT);
        guiCamera.setToOrtho(false, SCREEN_WIDTH, SCREEN_HEIGHT);
        if (isMobile()) {
            guiViewport = new ExtendViewport(SCREEN_WIDTH, SCREEN_HEIGHT, guiCamera);
        } else {
            guiViewport = new FitViewport(SCREEN_WIDTH, SCREEN_HEIGHT, guiCamera);
        }
...

and then (i have many screens), in screen i:

public ScreenLoader(Main main) {
    this.main = main;
    batch = new SpriteBatch();
    stage = new Stage();
    stage.setViewport(guiViewport);

..here i init and add actors. And don't forget to

@Override
public void render(float delta) {
    stage.act(delta);
    stage.draw();