HttpContext.Current.User.Identity.IsAuthenticated is always false

I am trying to recover the currently logged-in user on my system, but for some reason the IsAuthenticated property always returns a false :

I'm using this class to set the user to the context and to retrieve the logged-in user, which is in a class library project:

namespace Helper
{
public static class SessionHelper
{
    public static bool ExistUserInSession()
    {
        return HttpContext.Current.User.Identity.IsAuthenticated;
    }

    public static void DestroyUserSession()
    {
        FormsAuthentication.SignOut();
    }
    public static int GetUser()
    {
        int user_id = 0;
        if (HttpContext.Current.User != null && HttpContext.Current.User.Identity is FormsIdentity)
        {
            FormsAuthenticationTicket ticket = ((FormsIdentity)HttpContext.Current.User.Identity).Ticket;
            if (ticket != null)
            {
                user_id = Convert.ToInt32(ticket.UserData);
            }
        }
        return user_id;
    }
    public static void AddUserToSession(string id)
    {
        bool persist = true;
        var cookie = FormsAuthentication.GetAuthCookie("usuario", persist);

        cookie.Name = FormsAuthentication.FormsCookieName;
        cookie.Expires = DateTime.Now.AddMonths(3);

        var ticket = FormsAuthentication.Decrypt(cookie.Value);
        var newTicket = new FormsAuthenticationTicket(ticket.Version, ticket.Name, ticket.IssueDate, ticket.Expiration, ticket.IsPersistent, id);

        cookie.Value = FormsAuthentication.Encrypt(newTicket);
        HttpContext.Current.Response.Cookies.Add(cookie);
    }
}
}

After a validation of user and password vs my database I use the AddUserToSession method to set the user to the session, if I clean those lines I can see how the cookie and ticket are generated correctly .

This is the part of the Action where I send to call the mentioned method:

if (ModelState.IsValid)
    {
        _usuarioViewModel.Email = model.Email;
        _usuarioViewModel.Password = model.Password;

        var usuarioDomain = Mapper.Map<UsuarioViewModel, Usuario>(_usuarioViewModel);
        UsuarioDto usuarioDtoDomain = _userRepository.Login(usuarioDomain);

    //Si la autenticacion no fue exitosa la capa correspondiente regresa un CustomException
        if (usuarioDtoDomain != null)
        {
            SessionHelper.AddUserToSession(usuarioDtoDomain.UsuarioId.ToString());

            return View("~/views/home/index.cshtml");
        }

Well, until here everything is fine it logs and apparently sets the user Id to the context, the issue occurs when I ask for the authenticated user, from the view to show the username:

 @if (SessionHelper.ExistUserInSession())
 {
 <div class="row">
     <div class="col-xs-12 text-center well">
         Bienvenido, <b>@FrontUser.Get().Email</b> [<a href="~/home/salir">Finalizar sesión</a>]
     </div>
 </div>
  }  

As you can see, SessionHelper is a static class but for some reason when calling the function:

public static bool ExistUserInSession()
{
   return HttpContext.Current.User.Identity.IsAuthenticated;
}

This always returns false.

This is the corresponding section of the web.config.

<system.web>
<compilation debug="true" targetFramework="4.6" />
<httpRuntime targetFramework="4.6" />
<authentication mode="Forms">
  <forms name="prueba" cookieless="UseCookies" protection="All" />

</authentication> 
</system.web>

If someone with more experience can see something wrong, I will be very grateful if you inform me or offer a tip to find the source of my problem.