When a node leaves a scene and returns back, it is not rendered any more. Reproducible with following code:

    @Override
    public void start(Stage stage) {
        final Group root = new Group();
        Scene scene = new Scene(root, 500, 500, Color.BLACK);
        final Rectangle r = new Rectangle(0, 0, 250, 250);
        r.setFill(Color.BLUE);
        root.getChildren().add(r);
        
        TranslateTransition transition = new TranslateTransition(
                Duration.seconds(2), r);
        transition.setToX(550);
        
        transition.setCycleCount(Timeline.INDEFINITE);
        transition.setAutoReverse(true);
        transition.play();
        
        stage.setTitle("JavaFX Scene Graph Demo");
        stage.setScene(scene);
        stage.setVisible(true);
    }