Incoming UDP messages blocked for Netbeans IDE on WIndows 10

Question

For historical reasons I still use Netbeans 12.5 with several Java/JavaFx projects. I have a e-car charger connectet to my LAN via a switch. I have opened the necessary ports so by Using UDP Test Tool 3.0 I can send and receive UDP messages to/from the charger without problems. It also works with my Java app when I build a .jar and exexutes it from a command window (DOS prompt). So far so good!

But when I run the same code in the debugger in Netbeans 12.5 IDE, the incoming messages are blocked somehow. They never reach my message queue. I have tried to play around with permissions in Windows Defender / Firewall (no 3.rd party antivirus installed). But no success.

I have googled and searched in StackOverflow, but can't find any similar postings. Does anybody have a suggestion to what it can be and how I can fix it?

/*
* Click nbfs://nbhost/SystemFileSystem/Templates/Licenses/license-default.txt to change this license
* Click nbfs://nbhost/SystemFileSystem/Templates/javafx/FXMain.java to edit this template
*/
package listentest2;

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import javafx.application.Application;
import javafx.concurrent.Task;
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;

public class ListenTest2 extends Application {

private Thread listenThread;

Task<Integer> chargerListenerTask = new Task<Integer>()
{
    int noOfMessages = 0;

    @Override
    protected Integer call() throws Exception
    {
        updateMessage("Listener thread started");
        while (true)
        {
            if (isCancelled())
            {
                updateMessage("Listener thread cancelled");
                break;
            }

            try
            {
                //          Constructs a datagram socket and binds it to the specified port on the local host machine..
                DatagramSocket socket = new DatagramSocket(7090);
                System.out.println("UDP listener started on port 7090");

                // Buffer to hold incoming datagrams
                byte[] buffer = new byte[1024];

                while (true)
                {
                    // Create a DatagramPacket to hold the incoming datagram
                    DatagramPacket packet = new DatagramPacket(buffer, buffer.length);

                    // Receive the incoming datagram
                    socket.receive(packet);

                    // Extract the message from the datagram
                    String message = new String(packet.getData(), 0, packet.getLength());
                    InetAddress chargerAddress = packet.getAddress();
                    int senderPort = packet.getPort();

                    // Print out the received message and sender's address
                    System.out.printf("Received message: \"%s\" from %s:%d%n", message, chargerAddress, senderPort);
                }
            }
            catch (IOException e)
            {
            }
            updateMessage("Listener thread: Listen terminated");
        }
        updateMessage("Listener thread  finished");
        return 0;
    }
};

@Override
public void start(Stage primaryStage)
{
    listenThread = new Thread(chargerListenerTask);
    listenThread.setDaemon(true);
    listenThread.start();

    Button btn = new Button();
    btn.setText("Say 'Hello Listener'");
    btn.setOnAction(new EventHandler<ActionEvent>()
    {

        @Override
        public void handle(ActionEvent event)
        {
            System.out.println("Hello Listener!");
        }
    });

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

    Scene scene = new Scene(root, 300, 250);

    primaryStage.setTitle("Hello Listener!");
    primaryStage.setScene(scene);
    primaryStage.show();
}

/**
 * @param args the command line arguments
 */
public static void main(String[] args)
{
    launch(args);
}

}