The message says: "You have already purchased this but it isn't available for redownload. To purchase it again at full price, tap OK" Given the exact phrasing

The message says: "You have already purchased this but it isn't available for redownload. To purchase it again at full price, tap OK" Given the exact phrasing of the parts I highlighted, I don't think it is a bug. I cannot see in the picture what book it is, but since this does not happen to you for your books, it could be something related to copyright/distribution.