There a few possible scenarios in which the cart will be empty after a visitor clicks back to the site from a cart abandonment email.
When test emails are sent through the system the items that appear in them are a random selection from the site catalog and do not correspond to the actual cart content of the specific user who received the email. The items will not appear in the actual cart.
If a visitor clicks back to site from a different computer than the one that was used when the cart was abandoned then in most likelihood the cart will not recognize him as the same visitor and the cart will be empty. Barilliance cannot recreate the cart in this case (however, if your cart provider supports recreating the cart using a session id , Barilliance can store the session id and pass it as a url parameter. Please ask about this option if you know your cart provider supports this functionality)
If your cart software is set to expire the cart after a short while then it's possible that in the time a visitor clicks back from the email the cart will have already expired. The recommended solution in this case is to use the Send To Product Page option. When this option is selected any clicks on the items in the email will send the visitor back to product page instead of the cart. You may need to change the content of the email to reflect this change (change any text that says "click here to go back to the cart").