Products need to be grouped in Okendo by going to reviews > groups. You can search if a group exsists. If not click +New group.
Settings:

Group Type: Shopify
Click the collections link. Copy the phrase next to the missing item, "reviews-[PRODUCT NAME]". Search for that collection and select it
Check the toggle, "Automatically assign newly added products to display reviews from this group".
Press save

If the product exsists, you'll need to go into Shopify collections and search for the collection, "reviews-[PRODUCT NAME]" and figure out what went wrong.