Have you tried you looking in the All section of storage? The points-giving items for both the Leaderboards and the World Events only show up there, and not in the Deco section. Usually the item(s) are located about 3/4 of the way down the All inventory list.
This is an issue that has been reported many, many times. The items will not appear in inventory until after you force close and then reopen your game, and then the items only appear in the All section. If this doesn't work, you should submit a ticket to customer support to see if they can help.
https://support.storm8.com/hc/en-us
Because of all the reports, Storm8 must be aware of the issue. At this point, the only conclusions to be drawn are: they either can't fix it or they just can't be bothered to fix it.