Have you checked the transaction history to make sure it wasn't sent out or stolen? I had a near heart attack when I forgot I transferred some coin to another address once upon a time. It also could potentially just be a temporary bug in the UI that's just not letting you see it currently.. It's a long shot, and I don't really know much about hard wallets, but does the firmware or software need updating by any chance? It might have been programmed a little goofy and just needs an update or something simple like synchronizing it to the chain.