Nintendo has acknowledged the existence of a game-breaking bug in Pokémon X and Pokémon Y and is currently working on a fix.
The issue seems to be mainly affecting users in Europe and Japan and occurs when players save in Lumiose City — Miare City in Japan — causing an irreversible corruption to the save data forcing players to start over. Nintendo has provided a map of Lumoise City with information on where players should not save their game. Nintendo advises saving inside a Pokémon Center. You can view the map below.
The fix will be provided in an application that has to be downloaded from the eShop which will restore the corrupted save data. Expect the fix to arrive as soon as it’s available.
Via: Nintendo Life