Every item is linked to the uploader's email address. If someone changes the email of that account, all of the items disappear. This is because, as far as the system knows, the item's email address is not the same as the new email address.
What I find strange is that the uploader's email address is made public on every item they upload. This is not good, especially if someone uses an alias as their account name but has their full name as their email address. It would be surprisingly easy to scrape every email address from every uploader and cause a moderate leak of information.
Why can't they just relink all the content and force password resets? Something doesn't add up. Looking at the forums, it seems like someone is doing manual remediation.