Exception in thread "JavaFX Application Thread" java.util.ConcurrentModificationException

I am getting this error while trying to show stage in JavaFx, tried multiple available answers already but none of them worked.

My code

private void redirectToLogin() {
        try {
            Parent root = null;
            FXMLLoader fxmlLoader = new FXMLLoader(getClass().getResource("/view/login.fxml"));
            fxmlLoader.setResources(resourceBundle);
            root = fxmlLoader.load();
            Stage primaryStage = new Stage();
            new Thread(() -> {
                logger.info("Initializing tray icon");
                App.TRAY_ICON = new TrayIcon();
                App.TRAY_ICON.displayingTrayIcon(userService, downloadingService, schedulerService, primaryStage);
            }).start();
            primaryStage.setTitle(resourceBundle.getString("appTitle"));
            primaryStage.getIcons().add(new javafx.scene.image.Image(this.getClass().getResource("/images/test.png").toString()));
            Scene scene = new Scene(root, 800, 600);
        scene.getStylesheets().add(getClass().getResource("/css/test.css").toExternalForm());
            primaryStage.setScene(scene);
            primaryStage.setResizable(false);
            System.out.println("Calling show");
            primaryStage.show();
            System.out.println("show called");
            Platform.setImplicitExit(false);
        } catch (Exception e) {
            System.out.println("Exception in appinstall : "+e);
            e.printStackTrace();
        }
    }

Full Error stack:

Exception in thread "JavaFX Application Thread" java.util.ConcurrentModificationException
at java.util.HashMap$HashIterator.nextNode(HashMap.java:1429)
at java.util.HashMap$KeyIterator.next(HashMap.java:1453)
at com.sun.javafx.font.PrismFontFactory.removeEmbeddedFont(PrismFontFactory.java:1554)
at com.sun.javafx.font.PrismFontFactory.loadEmbeddedFont(PrismFontFactory.java:1638)
at com.sun.javafx.font.PrismFontFactory.loadEmbeddedFont(PrismFontFactory.java:1529)
at com.sun.javafx.font.PrismFontLoader.loadFont(PrismFontLoader.java:99)
at javafx.scene.text.Font.loadFont(Font.java:400)
at com.sun.javafx.css.StyleManager.loadStylesheetUnPrivileged(StyleManager.java:1001)
at com.sun.javafx.css.StyleManager.loadStylesheet(StyleManager.java:798)
at com.sun.javafx.css.StyleManager.gatherParentStylesheets(StyleManager.java:1285)
at com.sun.javafx.css.StyleManager.findMatchingStyles(StyleManager.java:1400)
at javafx.scene.CssStyleHelper.createStyleHelper(CssStyleHelper.java:115)
at javafx.scene.Node.impl_processCSS(Node.java:8877)
at javafx.scene.Parent.impl_processCSS(Parent.java:1250)
at javafx.scene.control.Control.impl_processCSS(Control.java:872)
at javafx.scene.Parent.impl_processCSS(Parent.java:1281)
at javafx.scene.Parent.impl_processCSS(Parent.java:1281)
at javafx.scene.Parent.impl_processCSS(Parent.java:1281)
at javafx.scene.Parent.impl_processCSS(Parent.java:1281)
at javafx.scene.Parent.impl_processCSS(Parent.java:1281)
at javafx.scene.Parent.impl_processCSS(Parent.java:1281)
at javafx.scene.Node.processCSS(Node.java:8732)
at javafx.scene.Scene.doCSSPass(Scene.java:569)
at javafx.scene.Scene.access$3500(Scene.java:201)
at javafx.scene.Scene$ScenePulseListener.pulse(Scene.java:2385)
at com.sun.javafx.tk.Toolkit$3.run(Toolkit.java:321)
at com.sun.javafx.tk.Toolkit$3.run(Toolkit.java:319)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.tk.Toolkit.runPulse(Toolkit.java:319)
at com.sun.javafx.tk.Toolkit.firePulse(Toolkit.java:348)
at com.sun.javafx.tk.quantum.QuantumToolkit.pulse(QuantumToolkit.java:479)
at com.sun.javafx.tk.quantum.QuantumToolkit.pulse(QuantumToolkit.java:460)
at com.sun.javafx.tk.quantum.QuantumToolkit$13.run(QuantumToolkit.java:327)
at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:95)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.access$300(WinApplication.java:39)
at com.sun.glass.ui.win.WinApplication$4$1.run(WinApplication.java:112)
at java.lang.Thread.run(Thread.java:745)

All paths/URIs are double-checked already i.e icon, CSS, and FXML exists at the there respective location.

Please help

You are accessing to a non cocurrent hashmap from different threads. If you need to access the same hashmap variable from different threads you must use :

https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ConcurrentHashMap.html

Maybe from displayingTrayIcon function?