.Net Framework Web Api SelfHost service stopped suddenly

Question

• I created a simple Web Api selfHost as windows service which listens to an address which is dynamically loads from the database and normally it includes port number( like : http://localhost:1900) When I change the address( for example port number, something like http://localhost:1901) the service can catch the requests on the new port but the requests on old port ( http:localhost:1900) leads to crashing the service and it will be stopped. I just could debug my service and saw just NullReference Error and not any more info about it. I don't know even where this error happened and non of my logs could help me. what do you think about this error? Have you ever seen this kind of error before?

• For more info I should say just some errors I can see in Event Viewer window :

• Application: {Service.exe} Framework Version: v4.0.30319 Description: The process was terminated due to an unhandled exception. Exception Info: System.NullReferenceException at System.Web.Http.SelfHost.HttpSelfHostServer+d__35.MoveNext() at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(System.Threading.Tasks.Task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(System.Threading.Tasks.Task) at System.Web.Http.SelfHost.HttpSelfHostServer+d__34.MoveNext() at System.Runtime.CompilerServices.AsyncMethodBuilderCore+<>c.b__6_1(System.Object) at System.Threading.QueueUserWorkItemCallback.WaitCallback_Context(System.Object) at System.Threading.ExecutionContext.RunInternal(System.Threading.ExecutionContext, System.Threading.ContextCallback, System.Object, Boolean) at System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext, System.Threading.ContextCallback, System.Object, Boolean)

• Faulting application name: {Service.exe}, version: 1.0.0.0, time stamp: 0xc594704b Faulting module name: KERNELBASE.dll, version: 10.0.14393.3383, time stamp: 0x5ddcb9ff Exception code: 0xe0434352 Fault offset: 0x000dc232 Faulting process id: 0x7370 Faulting application start time: 0x01d72886545b1d41 Faulting application path: {Service PhysicalAddress} Faulting module path: C:\Windows\System32\KERNELBASE.dll Report Id: 305c75f4-8c83-484a-b673-565abfc2b7d6 Faulting package full name: Faulting package-relative application ID

• For more details I bring my Service Class Body below :

  class service
   {
    HttpSelfHostConfiguration config;
    HttpSelfHostServer server;
    Timer _timer = new Timer();
  
    protected override void OnStart(string[] args)
    {
        _timer.Interval = 2000;
        _timer.Elapsed += _timer_Elapsed;
        _timer.Enabled = true;
    }
  
    private void _timer_Elapsed(object sender, ElapsedEventArgs e)
    {
        var listenToUrl = _getDestUrlFromDB();
        var configChanged = false;
        if (config != null && config.BaseAddress.AbsoluteUri != listenToUrl + "/")
        {
            configChanged = true;
            config.Dispose();
        }
        config = new HttpSelfHostConfiguration(uploadApiUrl.Data);
        config.Routes.MapHttpRoute("default",
                                    "api/{controller}/{id}",
                                    new { controller = "Home", id = RouteParameter.Optional });
        config.ClientCredentialType = System.ServiceModel.HttpClientCredentialType.Windows;
        if (server == null)
        {
            server = new HttpSelfHostServer(config);
            var task = server.OpenAsync();
            task.Wait();
  
        }
        else if (configChanged)
        {
  
            try
            {
                Process.Start("cmd", $@"netsh http add urlacl url={listenToUrl} ");
                Process.Start("cmd", $@"delete urlacl url={listenToUrl} ");
                server.Dispose();
                server = new HttpSelfHostServer(config);
                var task = server.OpenAsync();
                task.Wait();
  
            }
            catch (Exception ex)
            {
            }
  
        }
  
    }
  }