ADDITIONAL SYSTEM INFORMATION :
- Windows 10 Professional, 64-bit (10.0.18363.836)
- openjdk version "11.0.7" 2020-04-14 LTS
- OpenJDK Runtime Environment Zulu11.39+15-CA (build 11.0.7+10-LTS)
- OpenJDK 64-Bit Server VM Zulu11.39+15-CA (build 11.0.7+10-LTS, mixed mode)
- Intel UHD Graphics 620, driver version 26.20.100.7810 (also not working on 630, 26.10.100.7262)

A DESCRIPTION OF THE PROBLEM :
On certain systems, the same JavaFX application, which works fine on other systems, appear to have empty windows if StageStyle.UNIFIED is set.

Using the -Dprism.order=sw option solves the problem.

REGRESSION : Last worked in version 11.0.7

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
After clicking on "Open" a new window should open, rendering the provided label.
ACTUAL -
After clicking on "Open" a new window opens, rendering nothing.

---------- BEGIN SOURCE ----------
package com.example;

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.Label;
import javafx.stage.Stage;
import javafx.stage.StageStyle;

public class JfxRenderingIssue extends Application {
    @Override
    public void start(Stage primaryStage) throws Exception {
        final Button button = new Button("Open");
        button.setOnAction(event -> {
            final Stage stage = new Stage(StageStyle.UNIFIED);
            stage.setScene(new Scene(new Label("Label")));
            stage.setTitle("Window");
            stage.show();
        });

        primaryStage.setScene(new Scene(button));
        primaryStage.setTitle("Primary");
        primaryStage.show();
    }

    public static void main(final String... args) {
        Application.launch();
    }
}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
a) using -Dprism.order=sw
b) avoiding StageStyle.UNIFIED