Some browsers may 'time out' trying to render a large number of line items on a shopping cart page. The MaxCartItemsBeforeCheckout Setting can be configured to allow a maximum number of items. 

The default configuration for this setting is 300. To change the maximum number of line items in a shopping cart, go to Configuration > Settings in the AspDotNetStorefront admin console, and search for MaxCartItemsBeforeCheckout. Click the setting name to edit, change the value, and click Save and Close. Then click Refresh Store.