In Zoa and Minera theme, we use Variation Swatches for WooCommerce plugin to get better looking at variation. 

But from WooCommerce 3.5.1, it has the conflict, user cannot save the attributes when editing the product. 

In this case, please deactivate and delete Variation Swatches for WooCommerce plugin

download the fixed version here Source code(zip) and upload to your site