err_connection_timed_out after some successful calls in angularjs - angularjs

Question

I am using http service of AngularJs and it works successfully. But from last three months, I receive err_connection_timed_out after 1 or two successful calls. If I reload the page, then the error disappears.
I am using ASP.Net MVC as backend application and it uses Cookies for session management.
Anybody can help how to resolve this issue?
Global.asax.cs
protected void Application_BeginRequest(Object sender, EventArgs e)
{
HttpContext.Current.Items["dbkey"] = new DBEntities();
}
protected void Application_BeginRequest(Object sender, EventArgs e)
{
var entityContext = HttpContext.Current.Items["dbkey"] as DBEntities;
if (entityContext != null)
entityContext.Dispose();
}
LoginController
public JsonResult JsonLogin(string email, string password)
{
// Hashed ticket
string hashCookies = FormsAuthentication.Encrypt(ticket);
HttpCookie cookie = new HttpCookie(FormsAuthentication.FormsCookieName, hashCookies);
cookie.Expires = expiryDate;
Response.Cookies.Add(cookie);
HttpCookie mycookie = new HttpCookie("cookieName");
HttpContext.Current.Response.Cookies.Set(mycookie);
}
StaffController
protected override void OnActionExecuting(ActionExecutingContext filterContext)
{
HttpCookie cookie = HttpContext.Current.Request.Cookies["cookieName"];
if (cookie == null || string.IsNullOrEmpty(User.Identity.Name))
{
filterContext.Result = new RedirectResult("/Login/Index");
}
base.OnActionExecuting(filterContext);
}
public JsonResult GetData()
{
var res = entityContext.StaffData.Where(...).ToList();
return Json(res, JsonRequestBehavior.AllowGet);
}
Data.js
var app = angular.module('StaffApp', []);
app.controller('StaffCtrl', function ($scope, $http) {
$scope.GetData = function () {
$http.get("/Staff/GetData")
.then(function (response) {
let data = response.data;
if (data.length > 0) {
angular.forEach(data, function (fm, key) {
$scope.Staffs.push(fm);
});
}
}, function (response) {
});
};