PayPal Smart Checkout Button Disappears

When I enter the short code for the PayPal smart checkout button, it shows up for about 5 seconds and then disappears from the page entirely. I saw that someone had the same issue about 1.5 years ago and it was supposedly resolved by an update, but I have the latest version of WordPress and Simple Membership and I can’t get the button to stay on the page.

The page I need help with: [log in to see the link]