Unfortunately, if you're missing some of your legendary shards, then you or someone else did use them for purchases in some form within the game. There's no current wide-spread issue of currency going missing. Fortunately, there won't be an account rollback, so you're safe there. Bungie does not roll back individual save data. Unfortunately, Bungie also will not refund your unknown purchases and give you the legendary shards back. Sadly, you'll have to regain them the old fashioned way. - I know you feel that you didn't use them to purchase anything, but did you happen to buy several enhancement cores from Spider and don't remember? Those can get expensive quickly.