First TestFX test executed fails, identical second test passes, when in headless mode

Question

I have a problem with TestFX, and running in headless mode on my desktop PC with openjfx-monocle.

Everything was working fine in my first "hobby project" but now when doing this at work I ran into some problems with the main menu that we have.

So the main menu is built up of a MenuBar, which contains Menus and those contains menuItems. Link to image below.

The problem I ran into was when I wanted to open an About dialog, from the main window. This is done by clicking in the MenuBar on the Menu that say 'Help', which displays a dropdown list of menuItems and for the Help Menu we only have the 'About' option right now.

So to the actual problem. I get the error when trying to click on the 'About' MenuItem... so the 'Help' Menu is clickable.

The error I get is:

org.testfx.api.FxRobotException: the query "About" returned no nodes.
at org.testfx.api.FxRobot.queryVisibleNode(FxRobot.java:1107) at
org.testfx.api.FxRobot.pointOfVisibleNode(FxRobot.java:1076) at
org.testfx.api.FxRobot.clickOn(FxRobot.java:750) at
org.testfx.api.FxRobot.clickOn(FxRobot.java:60) at
se.compenayname.testfx.pages.AboutPage.openAboutDialogFromMain(AboutPage.java:46)

Now whats strange to me is that it works great for the next test that gets executed. So if I would create lets say an empty test, or a test which just does an assert for 1+1 = 2 and set it to run first then all tests would pass. - But I dont want to do that, something smells funny and I want to know what I am doing wrong.

Now are there anyone who have had this/similar problems before? or anyone that can help me out, and hopefully just point out some silly newbie misstakes that I've done and send me on my way :)

Additional information that you might need: OS: Windows 7. Editor: Eclipse. Gradle version: 3.3. JDK : 8u121.

The TestFX and Monocle dependencies in the build.gradle file are:

testCompile  "org.testfx:testfx-core:4.0.+", 
             "org.testfx:testfx-junit:4.0.+"
testRuntime  "org.testfx:openjfx-monocle:1.8.0_20"

I am note sure if anything else is needed, but I'll give this a try and post this. Apologies beforehand if I am missing something, or if I am unclear in any way.

The code I am running can be seen below.

public class AboutDialogTests extends TestFXBase{

    private AboutPage aboutPage;

    @Before
    public void before() throws Exception {
        aboutPage = new AboutPage(this);
    }

    @Test
    public void verifyCopyrightText(){
        aboutPage.openAboutDialogFromMain();

        FxAssert.verifyThat(AboutDialogFXIDs.COPYRIGHTLABEL, (Label copyrightLabel) -> {
            String text = copyrightLabel.getText();
            return text.equals("Copyright © 1995-2017. CompanyName AB. All rights reserved.");
        }); 
    }
    @Test
    public void verifyCopyrightText2(){
        aboutPage.openAboutDialogFromMain();

        FxAssert.verifyThat(AboutDialogFXIDs.COPYRIGHTLABEL, (Label copyrightLabel) -> {
            String text = copyrightLabel.getText();
            return text.equals("Copyright © 1995-2017. CompanyName AB. All rights reserved.");
        }); 
    }
}

Here is my simple TestFXBase class:

public class TestFXBase extends ApplicationTest{

    private Stage primaryStage;

    /**
     * Am always running in headless mode at the moment.
     */
    static{
        System.setProperty("java.awt.headless", "true");
        System.setProperty("testfx.robot", "glass");
        System.setProperty("testfx.headless", "true");
        System.setProperty("prism.order", "sw");
        System.setProperty("prism.text", "t2k");

    }


    @Override
    public void start(Stage stage) throws Exception {
         this.primaryStage = stage;
         primaryStage.show();
    }


    @Before
    public void beforeEachTest() throws Exception{
        /*
         *  The following FxToolkit lines allow for indirectly performing
         *  ApplicationTest.launch(Main.class); and registering the primary stage
         *  in order to allow running multiple @Test in a single file
         */
        FxToolkit.registerPrimaryStage();

        // specifying which class to start the application with.
        FxToolkit.setupApplication(Main.class); 
    }


    /**
     * Release any keys and mousebuttons that may be stuck so that it wont influence other tests.
     * @throws TimeoutException
     */
    @After
    public void afterEachTest() throws TimeoutException{
        FxToolkit.hideStage();
        release(new KeyCode[]{});
        release(new MouseButton[]{});
    }
    public Stage getPrimaryStage() {
        return primaryStage;
    }
}

And here is the AboutPage class:

public class AboutPage{
    private final TestFXBase base;

    public AboutPage(TestFXBase fxBase) {
        this.base = fxBase;
    }


    /**
    * Navigate through the main menu and open the 'About' dialog.
    */
    public void openAboutDialogFromMain() {
        base.clickOn("Help").clickOn("About", Motion.VERTICAL_FIRST, MouseButton.PRIMARY);

    // The lines below does not work at all when trying to click on a menu / menuitem.
    //base.clickOn(MainMenuFXIDs.MAINMENUHELP);
    //base.clickOn(MainMenuFXIDs.HELPMENUITEMABOUT);
    }


    public void closeAboutDialog() {
        base.clickOn(AboutDialogFXIDs.CLOSEBUTTON);
    }
}