ADDITIONAL SYSTEM INFORMATION :
macOs 10.14.6 (18G2022)

A DESCRIPTION OF THE PROBLEM :
his program demonstrates how a 3D object with a transparent gradient texture applied to it loses the gradient when the scene is regenerated

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Use attached program
 * Steps to demonstrate bug:
 * 1. Set DISABLE_WORKAROUND to true
 * 1. Run code and notice transparent gradient getting lighter from left to right
 * 2. Select "Rebuild" from the menu and notice how gradient vanishes, but transparency remains
 *
 * Steps to demonstrate work around:
 * 1. Set DISABLE_WORKAROUND to false
 * 1. Run code and notice transparent gradient getting lighter from left to right
 * 2. Select "Rebuild" from the menu and notice how gradient remains


EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Gradient should not go away.
ACTUAL -
Gradient stops working after scene is regenerated.

---------- BEGIN SOURCE ----------
import javafx.application.Application;
import javafx.application.Platform;
import javafx.event.EventType;
import javafx.scene.*;
import javafx.scene.control.Menu;
import javafx.scene.control.MenuBar;
import javafx.scene.control.MenuItem;
import javafx.scene.image.WritableImage;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.StackPane;
import javafx.scene.paint.*;
import javafx.scene.shape.Box;
import javafx.stage.Stage;
import javafx.stage.StageStyle;

/*
 * This program demonstrates how a 3D object with a transparent gradient texture applied to it
 * loses the gradient when the scene is regenerated.
 *
 * Steps to demonstrate bug:
 * 1. Set DISABLE_WORKAROUND to true
 * 1. Run code and notice transparent gradient getting lighter from left to right
 * 2. Select "Rebuild" from the menu and notice how gradient vanishes, but transparency remains
 *
 * Steps to demonstrate work around:
 * 1. Set DISABLE_WORKAROUND to false
 * 1. Run code and notice transparent gradient getting lighter from left to right
 * 2. Select "Rebuild" from the menu and notice how gradient remains
 */

public class GradientBug extends Application {
  private static final boolean DISABLE_WORKAROUND = true;
  private WritableImage texture;

  public static void main (String[] args) {
    launch(args);
  }

  // Build Camera
  private PerspectiveCamera getCamera () {
    PerspectiveCamera camera = new PerspectiveCamera(true);
    Group cameraXGroup = new Group();
    cameraXGroup.getChildren().add(camera);
    camera.setTranslateZ(-100);
    camera.setNearClip(0.1);
    camera.setFarClip(10000.0);
    camera.setFieldOfView(40);
    return camera;
  }

  private SubScene get3dScene () {
    Group root = new Group();
    Color color = Color.GOLD;
    Color trans = new Color(color.getRed(), color.getGreen(), color.getBlue(), .7f);
    // Create background object to show transparency
    Box back = new Box(600, 200, 10);
    back.setTranslateZ(1100);
    if (DISABLE_WORKAROUND || texture == null) {
      // Build Gradient Texture with Alpha Channel
      Stop[] stop = {new Stop(0, Color.BLACK), new Stop(1, color)};
      LinearGradient gradient = new LinearGradient(0, 0, 1, 0, true, CycleMethod.NO_CYCLE, stop);
      Scene aux = new Scene(new StackPane(), 512, 4, gradient);
      texture = aux.snapshot(null);
    }
    // Build foreground object using transparent gradient texture
    Box box = new Box(400, 400, 10);
    PhongMaterial material = new PhongMaterial(trans);
    material.setDiffuseMap(texture);
    box.setMaterial(material);
    box.setTranslateZ(1000);
    root.getChildren().addAll(back, box);
    SubScene subScene = new SubScene(root, 600, 600, true, SceneAntialiasing.BALANCED);
    subScene.setFill(new Color(0.0, 0.0, 0.0, 1.0));
    subScene.setCamera(getCamera());
    return subScene;
  }

  @Override
  public void start (Stage stage) {
    stage.setTitle("Gradient Texture Bug");
    BorderPane borderPane = new BorderPane();
    Scene scene = new Scene(borderPane);
    borderPane.setCenter(new Group(get3dScene()));
    stage.setScene(scene);
    MenuBar menuBar = new MenuBar();
    borderPane.setTop(menuBar);
    Menu menu = new Menu("Action");
    menuBar.getMenus().add(menu);
    MenuItem item = new MenuItem("Rebuild");
    menu.getItems().add(item);
    item.addEventHandler(EventType.ROOT, ev -> {
      try {
        Group grp = (Group) borderPane.getCenter();
        grp.getChildren().clear();
        grp.getChildren().add(get3dScene());
      } catch (Exception ex) {
        ex.printStackTrace();
      }
    });
    stage.initStyle(StageStyle.TRANSPARENT);
    stage.show();
    stage.setOnCloseRequest(e -> {
      Platform.exit();
      System.exit(0);
    });
  }
}

---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
See notes in code and in "Steps to Reproduce"

FREQUENCY : always