Add To Cart button not showing on variable products in Chrome or Safari

I have just discovered that the “Add To Cart” button will not show for my variable products – such as: https://www.halagear.com/product/hala-butterknife-double-bladed-paddle/ – when I view this site in Chrome and Safari. Everything works ok in Firefox.

Before I hit ‘post’ on this article, I turned off my W3 Total Cache plugin and it appeared to fix the problem. Does anyone know what part of W3 Total Cache would be causing this problem?

https://www.ads-software.com/plugins/woocommerce/