Hello,
It looks like you updated XStore Core plugin but left out of date theme version. Never update XStore Core plugin without theme update. Follow this article to update the theme – https://xstore.helpscoutdocs.com/article/63-theme-update
Also, custom changes in files of your child theme can be a reason for problems. Please check how the site works with the parent theme activated.
If you need our assistance, provide temporary wp-admin and FTP access.
Regards