Magento Ajax Popup by Hussey Codings is coming fine when the there is product item in the cart. While the product has been removed from the mini cart or there is no product item in the cart, then the mini cart is not coming/showing... But it should be come/shown the mini cart dropdown box with message "There is no item in this mini cart" in spite of there is no cart item.
And when the there is product item in the cart, then Magento Ajax Popup by Hussey Codings has been coming, not always, one time coming, another time not coming....in magento18.104.22.168
This extension is compatible upto 1.9.2 version so please contact hussey ccoding support team they will help in this issues.
If the issue still persists, you may try out this popup module that allows you to create fully customizable popups, put them any where on your site pages,