First of all, you are using out of date version of the XStore theme and child theme with customized woocommerce files http://prntscr.com/rzyqth Once we switch to parent theme I don’t see issues http://prntscr.com/rzysgy It looks that your customization caused the problem with the related products slider.
Actually, I would recommend you to create a staging site (full copy of the production) and update theme, plugins, WP there to latest versions and then check which of changed files causes the issue. Once everything is updated, the problem is fixed then move updated files to production site to be up to date.
