Keep in mind that your device might have run out of free space or is low on free space. Some devices automatically remove a game/content that is not used by an app to make some room.
How to solve it? Easy! Just open Papumba again while connected to a Wi-Fi network, then look for the game you want to download and tap on the down arrow icon to make a new download. Voilá! The game/content is ready to be used while offline.