You can "double" claim any of the rewards from the daily challenge by spam clicking. You can also tap with two fingers to sometimes claim both at once.
Note how I got a total of 6 mystery packs and 10m RC from todays gifts.
Looks like client/server side it's just incrementing a number and once you have a count of 3 or more it denies the reward.
You could use bitwise operators to encode bit flags into the reward count number to resolve this - or more so to resolve the inconsistency where you can overload the number and be unable to claim it.
Ideally the better fix would be to disable the button until it has processed whatever it needs to do - be it a server side validation or client side rewarding of items.