How to fix the product image thumbnails functionality
Full Page Zoom won't interfere with your theme thumbnail system.
However, we usually find installations where the thumbnails are not working properly due to some previous template edition or a bad/incomplete uninstall of a previous app.
You can always contact us for help but, if you are familiar with web technologies, you can also try to fix it by telling the app where your thumbnails are located within your HTML markup.
To do so, go to the app preferences page and navigate to Advanced preferences, and then to Selector preferences:
The thumbnails selector value must be a jQuery selector pointing to the thumbnail elements (either the image elements or the links which contain them). Please note that the selector must match all thumbnails.
You can also use a different selector for mobile devices if the theme markup is different on mobile.