Till now I have been using an external plugin for product gallery which is : WooThumbs for WooCommerce by Iconic. Just a while ago I uninstalled this plugin because I wanted to get back to default product gallery solution. To my surprise the product pages stopped displaying at all. This is clearly caused by the plugin deactivation because when I activate it again, the product page gets back.
Could you please help me to identify the reason. Here is the example of a product page which should display: