The fact that you bought 2 at the same time and one works as it should but the other doesn’t, one should logically assume the one that doesn’t work is defective from the factory. You paid the same price for 2 new, working units. That is not what you received.
Take (or send) it back to where you bought it and get another one. You deserve it. If it’s inconvenient to return it to your dealer, you can call SanDisk Tech Support about a warranty replacement. It’s usually quicker to deal with the seller though so soon after purchase.
