For the time being the BetterBackPacks plugin has been disabled.
Any and all items you have in your packs are preserved so do not discard the packs you have in chests or inventories. I am in progress of reporting the issue to the developer in an attempt to get this fixed in a timely manner.
If the issue can not be resolved I will look for a better, more up-to-date plugin but if this happens you will not be able to get the items from the backpacks as the issue at hand is a major duping glitch and few ne'er-do-wells have already duped keys and various other items and I can not risk further damage to the server.
Again I apologize for the loss of the backpacks but give me a week or so to get either a fix or a new plugin.
Thank you for your patience and understanding.