Important - click on BUY button makes a redirect to the shopping cart but cart is empty on PROD web-site

Hello

I can see that ALL my web-site visitors (except me, see details below) have the same problem - when user clicks on BUY button it goes to the Shopping Cart page but there is nothing about products in it - shopping cart is EMPTY! After that user leaves my web-site. In 100% of cases!

But when I open the web-site (local DEV copy and PROD) I can put a product into the shopping cart - after redirect I can see it there... But the rest of the users - cant' - I can see it as I can see what user is doing when user visits the web-site...

Here is a way I make a request:

                        <a class="learn_more2" onclick="AjaxCart.addproducttocart_catalog('@addtocartlink');return false;" style="width:100%">
                            Buy now
                            <span style="font-size:1.5em">
                                <i class="fa-shopping-cart"></i>
                            </span>
                        </a>

here is a way how I create addtocartlink variable:

@{
    //prepare "Add to cart" AJAX link
    string addtocartlink = Url.RouteUrl("AddProductToCart-Catalog", new { productId = 8, shoppingCartTypeId = (int)ShoppingCartType.ShoppingCart, quantity = 1, forceredirection = true });
}

This is a value of the addtocartlink variable: /addproducttocart/catalog/8/1/1?forceredirection=True

DETAILS:
I have 2 stores on the web-site - not sure about store #1 (site.com) but problem definitely exists on store #2 (subdomain.site.com).
Anonymous checkout is enabled. I'm using DEV version of NOP (source code from GitHub). On the store #2 (store with such kind of issue) I'm using custom template. The problem exists for different kind of browsers - it exists for Chrome (diff.versions), Firefox, IE, Edge etc. In DEBUG mode I can see that the request goes to the ShoppingCartController, method is AddProductToCart_Catalog

Have you ever meet with such kind of issue? And how can I solve it?

Thanks!