Hello,
Thanks for the reply.
As we can see the error comes from xstore-child/woocommerce/content-product.php:317 line of file , so check what custom changed did you make in the child theme. You can re-name the file, in this case, code from there will not be applied and you will see if the error was caused by your custom changes in the child theme or by something in our parent theme.
If the problem is in our theme code, we will help. Provide temporary wp-admin and FTP access.
Regards