Cookie issue - writes but not reads

using IE11 on a localhost. This works fine on an ASP.NET MVC application but not classic webforms ASP.NET.
I create a cookie like so:
HttpCookie cookie = new HttpCookie("MyCook"); cookie.Value = "5"; Response.Cookies.Add(cookie);
On the next request or even when I close the browser and navigate to a page that reads the cookie, there is no cookie found!
HttpCookie userCookie = Request.Cookies["MyCook"];
userCookie returns null.

any ideas why? Whats going on?