The addition doesn't appear to be consistently available, although some people report having success deleting the app and re-downloading it. The main limitation is simply the number of videos that support X-Ray. You can be sure it will pop up in Amazon originals like The Grand Tour or The Marvelous Mrs. Maisel, but you might not see it if you're watching a back catalog movie from a third party. It's still good to see parity, though, and it beats having to keep your phone by your side in case curiosity gets the better of you.