asp.net mvc form authenticate lose cookie session - asp.net-mvc

Question

asp.net mvc project when publish, it always lose session after 15-20 minutes.
my global.asax
enter code protected void Application_Start()
{
AreaRegistration.RegisterAllAreas();
ModelBinders.Binders.Add(typeof(decimal), new DecimalModelBinder());
RouteConfig.RegisterRoutes(RouteTable.Routes);
BundleConfig.RegisterBundles(BundleTable.Bundles);
FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
}
protected void Application_PostAuthenticateRequest(Object sender, EventArgs e)
{
var authCookie = HttpContext.Current.Request.Cookies[FormsAuthentication.FormsCookieName];
if (authCookie != null)
{
FormsAuthenticationTicket authTicket = FormsAuthentication.Decrypt(authCookie.Value);
if (authTicket != null && !authTicket.Expired)
{
var roles = authTicket.UserData.Split(',');
HttpContext.Current.User = new System.Security.Principal.GenericPrincipal(new FormsIdentity(authTicket), roles);
}
}
}
Login Method :
//clear any other tickets that are already in the response
Response.Cookies.Clear();
//set the new expiry date - to thirty days from now
DateTime expiryDate = DateTime.Now.AddDays(30);
//create a new forms auth ticket
FormsAuthenticationTicket ticket = new FormsAuthenticationTicket(2, login.EmailID, DateTime.Now, expiryDate, true, "Kullanici Bilgisi");
//encrypt the ticket
string encryptedTicket = FormsAuthentication.Encrypt(ticket);
//create a new authentication cookie - and set its expiration date
HttpCookie authenticationCookie = new HttpCookie(FormsAuthentication.FormsCookieName, encryptedTicket);
authenticationCookie.Expires = ticket.Expiration;
authenticationCookie.HttpOnly = true;
//add the cookie to the response.
Response.Cookies.Add(authenticationCookie);
Please help me. Im control on google developer tools. I see timeout 2018 but session is always losing redirect to login page.
Web Config:
<authentication mode="Forms">
<forms cookieless="UseCookies" loginUrl="~/user/login" slidingExpiration="true"></forms>
</authentication>