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If you save in Lumiose City you risk your game save being permanently corrupted. Don't do it until the game is patched.
It doesn't seem to be affecting everyone but a fair few people are suffering from this bug. Reports of saving near geometry (Taxis, trees etc) are high. You're best off saving in a building or away from the city.
(These don't work for me but may for you.)
Some people claim to be able to get out of the crashed state by pressing the home button several times.
Others claim that you can remove your SD card, boot the game, then reset your 3DS, reinsert the SD card and load the save.