Hi,

When I switch products by the prev/next buttons on product page and I choose varient, the add to cart button won't light up.

vipsfashion.nl/broeken/katoenen-broek-detail/

Hi,

what do you mean by "light up" ? You meant like "re-activating" ?

It does work just fine on our Live Demo though, open this product page: demo.flexiblewebdesign.com/cleanmart/index.php/vm-categories-2/flexv2-layout
and click PREV (which goes to a product that has "disabled" add to cart button until you choose a custom field)

so something with your Joomla must have been breaking things after the AJAX load is completed. The JS file that is responsible for those AJAX is this:
www.vipsfashion.nl/templates/gantry/js/dynupdate.js?vmver=8809

You may also want to to disable the AJAX loading for NEXT - PREV product navigation (which is not an ideal way, but at last it will work). To disable this option, open the Flexible VM2 Template plugin and disable this option: Enable AJAX loading

Regards.