EventHandler does not get triggered in .NET Core worker service app

I am trying to create OPCDA C# client with worker service template in .NET Core 3.1.

My goal is to read PLC tag value when DataChange event is triggered by OPC DA. The sample code I have created does the job properly in Console App (.NET Core 3.1) but when I utilize same code in Worker Service App (.NET Core 3.1), I found that it connects to OPC DA Server properly but the DataChange event does not call the method. I tried adding this code in

public override Task StartAsync(CancellationToken cancellationToken) {}

as well as

protected override async Task ExecuteAsync(CancellationToken stoppingToken) {}

but it does not trigger the event and there is no error.

This is my sample code:

using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;
using Opc.Da;
using System;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;

namespace SampleWorkerService
{
    public class Worker : BackgroundService
    {
        private readonly ILogger<Worker> _logger;
        private readonly IConfiguration _config;

        public Opc.URL url;
        private Opc.Da.Server server;
        private OpcCom.Factory fact = new OpcCom.Factory();
        private Opc.Da.Subscription groupRead;
        private Opc.Da.SubscriptionState groupState;
        private List<Item> itemsList = new List<Item>();
        string opcTopicName = "TopicName";

        public Worker(ILogger<Worker> logger, IConfiguration configuration)
        {
            _logger = logger;
            _config = configuration;
        }

        public override Task StartAsync(CancellationToken cancellationToken)
        {
                url = new Opc.URL("opcda://localhost/OPC Server");
                server = new Opc.Da.Server(fact, null);
                server.Connect(url, new Opc.ConnectData(new System.Net.NetworkCredential())); 
                //On Debug Server.IsConnected = true meaning server is connected properly
                groupState = new Opc.Da.SubscriptionState();
                groupState.Name = "Group";
                groupState.UpdateRate = 1000;
                groupState.Active = true;
                groupRead = (Opc.Da.Subscription)server.CreateSubscription(groupState);
                groupRead.DataChanged += null;

                Item item = new Item();

                for (int i = 0; i < listTagNamesFrmconfigFile.Count; i++)
                {
                    item = new Item();
                    item.ItemName = $"{opcTopicName}{listTagNamesFrmconfigFile[i].Name}";
                    itemsList.Add(item);
                }

                groupRead.AddItems(itemsList.ToArray()); // On Debug, Item list is added properly

          //groupRead.DataChanged += 
                       new Opc.Da.DataChangedEventHandler(GroupRead_DataChanged); //tried this
          /await Task.Run(() => groupRead.DataChanged += GroupRead_DataChanged); //tried this
          groupRead.DataChanged += GroupRead_DataChanged; 
// This line does not trigger method GroupRead_DataChanged which reads Item Values, THIS IS THE ISSUE (Same Code Works good in Console App)

            return base.StartAsync(cancellationToken);
        }

protected void GroupRead_DataChanged(object subscriptionHandle, object requestHandle, ItemValueResult[] values)
        {
            foreach (ItemValueResult itemValue in values)
            {
                objPLCTagInfo readPLCTagInfo = new objPLCTagInfo();
                readPLCTagInfo.Value = itemValue.Value;
            }
        }

protected override async Task ExecuteAsync(CancellationToken stoppingToken)
        {
             // I tried below commented code, the opcMethods.OPCRead has same code above but does 
                not trigger "groupRead.DataChanged"
            
             //OPCMethods opcMethods = new OPCMethods();

            //while (!stoppingToken.IsCancellationRequested)
            //{
            //    //_logger.LogInformation("Worker running at: {time}", DateTimeOffset.Now);

            //    opcMethods.OPCRead(_config);

            //    await Task.Delay(1000, stoppingToken).ConfigureAwait(false);
            //}

        // Following code also doesnot trigger "groupRead.DataChanged"
          
            groupRead.DataChanged += (object subscriptionHandle, object requestHandle, 
                                           ItemValueResult[] values) =>
            {
                Console.WriteLine("Event Triggered");
            };

            // await Task.CompletedTask;

            await Task.Delay(1000, stoppingToken).ConfigureAwait(false);
        }

public override Task StopAsync(CancellationToken cancellationToken)
        {
            return StopAsync(cancellationToken);
        }

    }
}

Above Code works good with Console App. The event groupRead.DataChange does not trigger the method "GroupRead_DataChanged" to read the data, there is no error/exception occurs:

This Code Line and following method reads item values, which I am trying to make it work

groupRead.DataChanged += GroupRead_DataChanged;

protected void GroupRead_DataChanged(object subscriptionHandle, object requestHandle, ItemValueResult[] values)
    {
        //logic here to read item values
        foreach (ItemValueResult itemValue in values)
            { ... }
    }

I hope I have explained the issue I am trying to address.

I appreciate your time and solution provided in advance !