Hi,
This is Ecwid support.
Thank you for the details. We’ve inspected your site.
As far as I can see, the issue you discovered is caused by the theme used on the site (or some third-party plugin) and the way how pages are navigated. The site uses an AJAX-based page opening approach – when a page opens, its content is sent to the browser in the background by the means of JavaScript functions working in the page.
Ecwid is also an AJAX solution, it works on the same principles. Almost every aspect of Ecwid’s storefront (including the thumbnail and Add to Bag button in the single product widgets) is dependent on the presence and execution of Ecwid scripts in the correct order.
Unfortunately, some AJAX-based WordPress themes proved to be unable to run the set of scripts behind Ecwid for a correct work of the widgets. However, in some cases, one can overcome such issues. Do you have any option in your settings to disable the transition effect (AJAX loading)? Can you please try to disable it?
I think I could also look for the ways how to do it in your theme. Is there any chance I can get a copy of the theme for installing on my test WP site? Is it a custom-developed one or I can download it somewhere on the web?