I checked the issue on our test server but didn’t find any problem. The button from the product element works fine on small and desktop devices.
I checked your site and I think it is a cache issue. Can you please try deactivating the WP Super Cache plugin which you are using? Also, try deleting the cache from this plugin. Once cleared, reload your site in a Private window or in Incognito mode and check if you are still facing the issue.
If you are still facing the issue, try deactivating all the plugin from your site to check the issue.
Try it and let me know if you are still facing the issue.