see code in its contructor:

    public ProgressBarSkin(ProgressBar control) {
        super(control);
        ...
        control.widthProperty().addListener(observable -> updateProgress());
        ...
    }

may lead to memory leaks if skin is updated. Options to fix are using a weakInvalidationListener or keep a reference to the strong which is removed in dispose or switch to using changeListener registered via skin's changeListener api