If your longsword disappeared, replay the level that gives it to you. There seems to be a strange bug deleting gained (not bought) items, which will be tackled soon.
You can find which level gives which item here.
If more than one item disappeared, please write a new Topic and label it as BUG. Add to which level you got (so we can see which items you should have) and if you bought any items (especially if those are missing as well).