The very first New Leaf cartridge I bought died after about two years of playing it.My game didn't start crashing and I didn't get any warning messages...it just wouldn't load one day and kept getting stuck on the red and black Nintendo logo screen.I Googled for what might have happened to it and it turns out that the motherboard can go bad after a while.The game save is still intact but the cartridge can't be played anymore when that happens.So,I also discovered that you can transfer your game save from a bad physical copy to a digital copy which is what I did.I've been playing my first New Leaf town,Catlips,on a digital copy since then.I'm not sure if this is what happened to your game but it's a possibility.
Whattt! That?s awesome to know... if I already have second town digital copy will it overwrite that town if I save a digital copy from my cartridge?