As of the bundle patch, there was initially a bug where bundles could be stacked within bundles. This was subsequently fixed, but prior to that, there was a user who stacked bundles 100+ levels deep on an account, which when said user logged back in now caused a stack overflow, causing corruption to nearby memory in the server.
Unfortunately, despite spending a couple of hours trying, I could not repair the affected memory region to an extent where the server state was saveable, so I have been forced to not save said state, which means the game will be starting back up from the last-saved state, which is what we refer to as a rollback. The main problem with rollbacks, even more than losing the last bit of gameplay, is that different parts of the state are saved at different times, which causes the saved state to become inconsistent. For example, if you picked up an item from a container into your inventory, and it turns out that the character was saved after that, but the container wasn't, the item will have been duplicated, whereas if the opposite is true, the item will have been permanently lost. Most parts of the game state is usually saved somewhere between 0-2 hours prior to the crash, so that is about the timespan that can be expected to be affected.
I can't sufficiently express my apologies for letting this happen, but at this point there is unfortunately not a whole lot I can do about it, and there is also no way for me to validate claims of lost things.
To avoid similar problems in the future, I have installed a stack checker at some potentially deeply recursive algorithms, and will also be auto-purging any remaining deeply nested bundles that may have lingered.