I've inspected your site. This issue is most likely caused by the fact the your server for some reason restricts HTTP requests to app.ecwid.com .
Ecwid plugin for WordPress uses Ecwid APIs for retrieving product information from Ecwid servers (it is needed for SEO purposes). For that, the plugin has to make HTTP requests in background to the remote Ecwid servers at app.ecwid.com . If such requests are blocked by the server where the site is hosted then the plugin may work improperly. It seems like in your case the same thing happens.
Please contact your hosting provider on this matter - please ask them whether there are some problems with outgoing connections to app.ecwid.com . Maybe, there are some firewall rules affecting those connections or something else.
Meanwhile, as a workaround, please disable the plugin and integrate your store on some page of your site using the approach described in this article (please see the part 'Manual installation'):
Look forward to your comments.