WP Ultra Simple Shopping Cart Glitch

Since September 28, 2014, my customers can only put one item in the shopping cart at a time. If they try to add a second item, the cart shows only the most recent item clicked. They then must pay for that item and return to purchase a second item. My website is https://www.eqhrcenter.org. Also, it does not matter if the cart is on the post or in the widget, the same thing is happening. If anyone has a solution, please write back.