[Risolto] all the products on the site (hundreds) are shown in that field

In our product pages, most products have "linked" or "related" products added in the "upsell" field. These products are shown to the right in the product page, under "Similar products". This info is added by means of the Toolset template "Instrument".

Now for some reason in some product pages in the translated version this looks correct, the related products are shown as they should. But in other product pages, all the products on the site (hundreds) are shown in that field. This makes the page load very slow. So why does it work in some pages and not in others?