This case doesn't only happen in FT1. Every dungeon does. The only solution if you can't find any loots after opening the chest is to just restart your client and then continue the dungeon. You will see the loots lying on the floor. (Except CA 1 - 6 because after breaking the chests, dungeon automatically finishes. So if there are no loots, then its bad luck for you. LMAO)