Hello,

Sorry for the inconvenience but as far as we have confirmed from the Test Site, the Slider for the Related & Upsells is working fine. Here is one of the Product from Test Site to check for you: https://blackpearlspro.com/woodmart_support/product/new-simple-product-copy/

So, there isn’t any issue at the Theme level as you can see from the above Product.

Your earlier provided WP-ADMIN Login details aren’t working now. Could you please take complete Backup of your Site first, then provide us the WP-ADMIN Login details of your Site in the Private Content field along with the permission to completely debug your Site which includes deactivating all the third party Plugins and removal of on-Site Customization changes too, so that we can thoroughly check this issue on your Site and assist you accordingly.

Best Regards