Hello, Peter,
You have provided the text of warning and the child theme is mentioned there, which means the problem in the custom code of the child theme. In your case, archive-product.php file of the child theme is no longer compatible with the latest version of WooCommerce, to fix this, you need to compare 2 files (from the parent theme and from the child theme with your changes) and add the missing code to your child theme file https://text-compare.com/
The way of updating the XStore parent theme and XStore Core plugin doesn’t play any role in your current case (it can be done via FTP of via the Dashboard).
Kind Regards,
8theme team