Microsoft said that it has known the primary cause of the bug that deleted files for some users who firstly installed Windows 10 version 1809. Then, it has rolled out an update to Windows Insiders to fix the data deletion bug in October 2018 Update.
Microsoft Releases Fix for Data Deletion Bug in October 2018 Update
Files Get Lost after Upgrade to Windows 10 1809
As is well known, Microsoft rolled out its Windows 10 October Update to Windows users all over the world on October 2. However, many customers complained about files missing after the update on some forums like Reddit, Microsoft's own forums or Twitter.
In a blog post, the company said the number of customers who had installed the update was small and only one one-hundredth of one percent of users were affected by the bug.
When meeting the issue Windows 10 October 2018 Update wipes user data, Microsoft advised anyone affected by the bug to contact its support team. Besides, retrieving files from a backup, and using data recovery software to recover deleted files are recommended.
Meanwhile, it is necessary to use affected PCs as little as possible and minimize disk activity to maximize the chance of a successful recovery.
To investigate and fix data deletion bug in October 2018 Update, Microsoft has halted the rollout of Windows version 1809. However, just a few days later, Microsoft claimed that it has identified the rare bug causing data deletion in the update and it is rolling out a fix to members of the Windows Insider Program.
Microsoft Releases Fix for Data Deletion Bug after Finding Underlying Cause
According to John Cable from Microsoft, the reason for the original file deletion occurred to involve a problem with Known Folder Redirection (KFR) in Windows 10. KFR had been enabled previously but some files remained in the original location.
In Windows 10 April 2018 Update, some users with KFR reported an extra and empty copy of Known Folders on their devices. Thus, based on users' feedbacks, Microsoft tried to delete these empty and duplicate Known Folders in October 2018 Update.
Sad to say, this change plus another change to the update construction sequence resulted in deleting the original old folder location and content instead, only leaving the new active folder intact.
Let's see an example to learn it well. You moved Documents folders to a new location from its location in the user profile, some files still remained in the old place. Then, the setup logic for Windows 10 October 2018 Update removed this folder in the old location and all its files.
Besides, some users may also face this issue when using the Auto Save feature of OneDrive to relocate the contents of the Pictures, Desktop, Documents, and folders to corresponding locations in the cloud.
Microsoft said in its blog post "We have fully investigated all reports of data loss, identified and fixed all known issues in the update, and conducted internal validation."
But Microsoft hasn't made the fix version update available to the public. To start with, it will first release this update to Windows Insiders to ensure it won't have any problematic influence on its own before the release to wider Windows users.