The issue seems to be caused by the fact that “Newest” uses the createdAt sorting key. Using publishedAt seems to give the intended result (= newest published products).
I’m guessing that sorting using createdAt uses the listing creation time to sort, which means the longer the time spent between listing creation and listing publishing, the less likely the product is to appear on the “Newest” page.
In the meantime, for people who want to see the actual new products, here’s the link I’m using: