Unable to add product to cart after variant change (greys out)

[ElegantPress]

When someone tries to add this product or any other one that has a variant to it, the add to cart button greys out sometime and will not allow adding it. There are sometimes where this will work correctly but more times it doesn't. I am using the refresh theme. This has also happened on the dawn theme.

Product: Custom Printed DTF Transfers – Elegant Press Custom Prints & Tees (epcustomprints.com)

Any help on this would be appreciated.