Oh I see – your first screenshot was the ranked list that you see when you click the neck slot on your Best in Bags result, it wasn’t the list from the Add to My Bags upgrade finder result.
Those ranked lists won’t always match because they use different ranking algorithms. The list that you see when you click on your next slot in the Best in Bags result does a fast and simple ranking: leave all of your other stuff the same, and swap in that necklace. Show the score difference. This ranking method is also used for most Upgrade Finder searches as well, where several hundred items need to be ranked all at once.
Add to My Bags does a far more intensive ranking. It adds a new item to your inventory, and then it does a full Best in Bags optimization with that item available as an option. It then shows you whether your score would go up or down were you to obtain that item. This type of ranking takes a lot more time to run, thus why we made a special function for it with a limit of 10 items. You can read more about how Add to My Bags ranks things in this post:
(This post was written for the Great Vault search on the retail site, but it works the same as the Add to My Bags search.)