Woocomerce swap variant image not working

I have a product page which shows various dresses in different colours.

We are using the premium paid plugin called “Variation Swatches for WooCommerce” by getwooplugins.com

The user can select the colour dress they want and that puts a tick over the variant.

It is also supposed to swap out the main image with the variant image.

But it’s not.

I contacted the plugin developer and they say that when they switch to the default theme, it works so it must be a theme issue.