WP eCommerce Plugin, need help…

I’m using the wp-ecommerce plugin by Instinct and I’ve got a couple issues I urgently need help with. This is the first of the two:

When a customer adds a product to their cart and then refreshes or navigates to another page (including checkout) the product no longer appears in the their cart and stays it’s empty.

https://pro-ad-co.theportlandco.com/store

PS I disabled all of my plugins on the site and then tested the cart and still encountered the issue. I also deactivated all the plugins and switched the site theme and still encountered the issue. After that I also deactivated the custom theme and tried the default theme.