When you “Claim” the game, then go to the game’s home page and click on the “Download” button next to the “You own this game” message at the top, there is nothing to download.
You can only download the game when you first buy it, but if you come back after you will be unable to download it again, so it looks like you have something set up wrong.
Either change it to “Download only” during the sale, or enable the ability to download the game from the “claimed” page even after the sale is over.