Maybe not a lost feature, most likely just a change in the way settings work.
The button disappears 'upon successful download' when your 'remove download list items' prefeference is set that way. See below.. and set 'remove download list items' preference to either 'when safari quits' (like you see beow) or 'manual.' Then the button will persist, and you can find the item easily until you quit safari .. or remove all items from the list manually .. depending on which of the two settings you choose.
I like the 'quit safari' option, because I don't have to do anything to keep the list small and usable; it is cleared out every time I quit safari. And the files themselves persist in my downloads folder if I need to go find them later.