I understand that you have inquiries regarding the format of your Ultra 64GB microSD memory card.
Please, allow us to inform you that storage devices of 64GB and above are natively formatted in exFat. Fat32 has a size limitation and the card may be recognized as 32GB instead of 64GB if you format it in Fat32.
A storage device of 64GB is better to be formatted in exFat. Formatting the card in Fat32 does not mean though that you will lose the warranty.
SanDisk has been made aware of potential product issues involving a very small percentage of its 32GB and 64GB SanDisk Mobile Ultra microSD cards. Under certain circumstances the cards may lock up and the card becomes inaccessible. The issue has been identified and a manufacturing fix has already been put in place.
SanDisk stands behind its products and any customer who experiences this issue with microSDHC cards will be offered a replacement as long as the card is within warranty.