ADDITIONAL SYSTEM INFORMATION :
OS: Solus 4.1 Fortitude 64-bit
JVM: Eclipse OpenJ9 14
JavaFX 14

A DESCRIPTION OF THE PROBLEM :
Given enough clicks of the Button, the sample application sometimes fails to render ContextMenu, however it is still clickable - which this sample code does not exactly illustrate (I can confirm from another application).

This never happens on Windows.

Note that I have a relatively low-end laptop should it matter.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Just click the button enough times in the sample application under Linux.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
The ContextMenu should always display upon button click (when the button is enabled).
ACTUAL -
Sometimes, the button is disabled and the ContextMenu is NOT displayed - and the text says "showing".

I can confirm from my other application that the ContextMenu actually IS there, and it responds to mouse clicks.

---------- BEGIN SOURCE ----------
import javafx.application.Application;
import javafx.geometry.Side;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.ContextMenu;
import javafx.scene.control.Label;
import javafx.scene.control.MenuItem;
import javafx.scene.layout.HBox;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;

public class Test extends Application {

    @Override
    public void start(Stage primaryStage) {
        primaryStage.setTitle("Hello World!");
        Button btn = new Button();
        btn.setText("Show ContextMenu");

        Label label = new Label();

        ContextMenu ctx = new ContextMenu();
        ctx.getItems().add(new MenuItem("First"));
        ctx.getItems().add(new MenuItem("Second"));
        ctx.getItems().add(new MenuItem("Third"));
        ctx.getItems().add(new MenuItem("Fourth"));
        ctx.getItems().add(new MenuItem("Fifth"));

        ctx.setOnShown(e -> {
            label.setText("Showing");
        });

        ctx.setOnHidden(e -> {
            btn.setDisable(false);
            label.setText("Not showing");
        });

        btn.setOnMouseClicked(ec -> {

            btn.setDisable(true);

            ctx.show(btn, Side.BOTTOM, 0.0, 0.0);
        });

        HBox box = new HBox();

        StackPane root = new StackPane();
        root.getChildren().add(box);
        box.getChildren().add(btn);
        box.getChildren().add(label);

        primaryStage.setScene(new Scene(root, 300, 250));
        primaryStage.show();
    }
}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
I know of no workaround.

FREQUENCY : occasionally