Woocommerce product variations not working

As described in this thread on the Woocommerce forum, product variations were not appearing on my published items: https://www.ads-software.com/support/topic/variations-not-working-14/

A solution was to add this code to my custom css, as the opacity was 0.

.woocommerce-ordering select,
div.product form.cart .variations td.product_value select {
  opacity: 1 !important;
}

Is this behavior caused by Virtue?