I had the same issue on 2 sdcards bad thing that om my own I didn't make a backup. But om my gf sdcards i did.
Somehow it corrupts the card, after changing it back to our note 2 they were readable one time, after that I couldn't access it anymore. After that I just formated the cards and they both work perfectly on our phones.
Sent from my D6503 using XDA Premium 4 mobile app