If I win a contest (top 3 finish), often the prize awarded is unlimited something (lives or some types of candy) for 1 or 2 hours.
If I don't have an hour or two to spare just then, I will close the app (playing on iPhone) without selecting the "Claim Prize" button. If I return to the game several hours later, the "Claim Prize" screen is again presented, but selecting it then does nothing. This has happened two or three times, so would seem to be consistent behaviour.
Not looking for rewards - just reporting a glitch that needs fixing.