Modal Popup Add to Cart Freezes on Products with No Variants

[ZoBabe]

JM: 2.5.14
VM: 2.0.22a

Most items on the site have numerous stockable child products, and the modal popup works fine for those. However, any simple item with no variants just get hung up forever. (loading symbol shows, but the popup never opens). One other sites, where all the products are simple/no-varients, this has not happened.
  The item still gets added to the shopping cart page, so it isn't the end of the world, but it is an irritating little malfunction. I have tried changing the template to Bees5, and it still does the same thing.
https://www.sweetskins.com/jewelry/bali-hammered-hoops-detail.html
  (on some other items, I have used a pain-in-#@% work around of adding a dummy child product, and then setting the field to "display: none;" this makes it work OK on the front-end, but is a lot of extra steps just to get a pop-up working)
  Don't know if anyone can help figure it out, but thought I'd report it as it does seem to be a bug.