Hello Honza,
Thank you for contacting us and for using XStore.
1/ We do not give a guarantee for full theme compatibility with all existing 3rd party plugins. Sometimes, not always, you need additionally customize the theme or plugin to make them work together. Unfortunately, it’s not possible for the author to make the theme compatible with all the existing plugins and additional customization is outside the scope of our basic support.
2/ How it works with the default WooCommerce theme – Storefront activated on your site?
3/ Try to disable “Ajax Add To Cart” via Theme Options and check how it works then.
Thank you for your cooperation and we look forward to hearing from you soon.
Kind Regards,
8theme team