Have you activated XStore Core plugin?
Try to disable all the third-party plugins that do not come bundled with our theme https://xstore.helpscoutdocs.com/article/36-included-plugins and check if you still have the problem. Do not forget to clear cache or even disable it temporary.
Let me know the result.
Also, provide temporary wp-admin and FTP access – http://prntscr.com/nh9pq2
