It could be different things and I don't doubt you are having a problem. As mentioned in another reply, stones do 'disappear' temporarily when making a stake, being subtracted from your balance until confirms finish, though showing up under 'stake' in the meantime. Perhaps that's it, in which case it will (would have already) self-corrected assuming your are getting synced. Or maybe your wallet got buggered locally in some way, but you can probably reconstitute it with a new install and file backups from the previous one (which hopefully you have). If the coin itself had gone awry, this would be known and they'd already be worth penguins. It does occasionally happen that a POS payout arrives but does not confirm. Don't believe that's the root of your problem, but may be worth mentioning since it is a potential source of confusion.