We do not give a guaranty 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.
Describe in more detail with screenshots how it works with the default theme and what exactly is incorrect when XStore is activated. Also, you can contact the support of the plugin and ask for help from their side also.