ADDITIONAL SYSTEM INFORMATION :
JavaFX 17, Windows 10, JDK 11

A DESCRIPTION OF THE PROBLEM :
JavaFX 17.

When a display where we show the application is unplugged, the application moves to another display and JavaFX fails to recognize it.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
1. Have two monitors with two different scaling factors: A and B.
2. Open a JavaFX application on a monitor A.
3. Unplug the monitor A.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
The application is physically moved to the monitor B and it's rendered with the scaling factor of the monitor B.
ACTUAL -
The application is physically moved to the monitor B, but it's rendered with the scaling factor of the monitor A.

---------- BEGIN SOURCE ----------
import javafx.application.Application;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;

// Nothing special here, a simple application with a button.
public class SmokeTest extends Application {
    public static void main(String[] args) {
        launch(args);
    }

    @Override
    public void start(Stage primaryStage) {
        primaryStage.setTitle("Hello World!");
        Button btn = new Button();
        btn.setText("Say 'Hello World'");
        StackPane root = new StackPane();
        root.getChildren().add(btn);
        primaryStage.setScene(new Scene(root, 300, 250));
        primaryStage.show();
    }
}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
No workaround found. But moving the window towards the edge of the screen helps.