User blog comment:Sim533/Forgotten Ruins Bug/@comment-3083541-20140921172712/@comment-2233791-20140922075800

Cooldown has come somewhere begin August. Once you have played an epic dungeon or pocket adventure, there's a cooldown of 22 hours.

All the comments make it very clear that this is about a secret hidden easter egg instead of a bug. Although that the unlimited runs are a bug though.

You need 8 minifigures to enter the Medieval area. This one is true. If you have less than 8 minifigures then it can become a hard time for you to collect 8 minifigures with only the Pirate World available. The Pocket dungeons give good parts, the epic dungeon good loot (diamonds, stars) and the Piratto Grotto gives rare parts from time to time. You can collect 6 minifigures in the Pirate World, so it might become very hard to collect 8 minifigures, as there are only 6 to collect. After you have 8 minifigures, the game become very easy as there's is more possibilites.