I said this error happens on product builder, so i don’t think url is relevant, but okey.
Heres you see default template with related products option: https://ibb.co/4mxd4GB
heres the product page templates: https://ibb.co/7SLV6MD
How look like a builder on any template page: https://ibb.co/MkbdMKt
So if you scroll right the bottom of useable panel, you never see the related products on it. But its work fine on default page.
some url:
https://borocoffee.com/kategoria/single-origin-termekek/ (any product)
https://borocoffee.com/kategoria/blend/ (any product)
https://borocoffee.com/kategoria/kavekapszula/ (any product)