Wpf Desktop Api call duration more longer than actual api response time about 8-10 seconds

Here is case: I have wpf application on about 80 clients and they communicate single .net framework api for data process. I have stopwatch tracker some places for tracking durations on Wpf and api apps. Code samples :

My api attribute :

public class DurationControlLoggerAttribute : ActionFilterAttribute
{
    public override void OnActionExecuting(HttpActionContext actionContext)
    {
        var controller = actionContext.ActionDescriptor.ControllerDescriptor.ControllerName;
        var action = actionContext.ActionDescriptor.ActionName;

        actionContext.ActionArguments.Add("_stopwatch_", Stopwatch.StartNew());
    }

    public override void OnActionExecuted(HttpActionExecutedContext actionExecutedContext)
    {
        if (ConfigurationManager.AppSettings["ApiLogger"].ToLower().Trim() != "true")
            return;

        var controller = actionExecutedContext.ActionContext.ActionDescriptor.ControllerDescriptor.ControllerName;
        var action = actionExecutedContext.ActionContext.ActionDescriptor.ActionName;

        var stopWatch = (Stopwatch)actionExecutedContext.ActionContext.ActionArguments["_stopwatch_"];

        stopWatch.Stop();

        var scope = actionExecutedContext.ActionContext.Request.GetDependencyScope();
        var commonService = (ICommonService)scope.GetService(typeof(ICommonService));
        commonService.InsertLog(new Model.Common.LogModel
        {
            InsertDate = DateTime.Now.ToString(),
            LogLevel = "API",
            MachineName = "API",
            Message = $"Controller : {controller} - Action : {action} - TotalSeconds : {stopWatch.Elapsed.TotalSeconds}",
            StackTrace = string.Empty
        });
    }
}

Action sample :

    [HttpPost]
    [DurationControlLogger]
    public bool InsertProduct(ProductModel model)
    {
        return _mainService.TracingService.InsertProduct(model);
    }

This action process duration is about 0,03 seconds. On the other hand, wpf api call duration is about 10 seconds. Wpf code blocks are down below:

            var Stopwatch = Stopwatch.StartNew();
            var isSuccess = DataHelper.InsertProduct(Product);
            Stopwatch.Stop();
            if (Stopwatch.Elapsed.TotalSeconds > 2)
                DataHelper.InsertTraceLog($"ProducrtBusiness - InsertProduct TotalSecond : {Stopwatch.Elapsed.TotalSeconds}");

DataHelper.InsertProduct method does basic http post request. Code is here :

public static class HttpClientHelper
{
    public static T Post<T>(object model, string url)
    {
        var resultStatus = false;
        T resultData = default(T);

        using (var client = new HttpClient())
        {

            client.DefaultRequestHeaders.Accept.Clear();
            client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));


            var content = new StringContent(JsonConvert.SerializeObject(model), Encoding.UTF8, "application/json");

            HttpResponseMessage response = client.PostAsync(url, content).Result;

            if (response.IsSuccessStatusCode)
            {
                string data = response.Content.ReadAsStringAsync().Result;
                var result = JsonConvert.DeserializeObject<T>(data);
                resultStatus = response.StatusCode == System.Net.HttpStatusCode.OK;
                resultData = result;
            }
        }
        return resultStatus ? resultData : default(T);
    }
    .....

Does anyone has any idea about that situation?

EDIT

I add one last log code. Here is code: ` var stopwatch = Stopwatch.StartNew();

            HttpResponseMessage response = client.PostAsync(url, content).Result;

            stopwatch.Stop();
            if (stopwatch.Elapsed.TotalSeconds > 2)
            {
                AppendToFile($"{DateTime.Now.ToString()} - {model.ToString()} - {stopwatch.Elapsed.TotalSeconds} - Content: {jsonData}");
            }

`

This log duration still sometimes is 8-10 sec.