The users who got hit with the file loss typically had selected "Check for Updates" within the Settings area of Windows 10, which immediately initiated a delivery of new updates to their systems, including an installation of version 1809. "We expect this will allow us to better monitor the most impactful issues even when feedback volume is low", Microsoft says.
An updated version of the Windows 10 October 2018 Update is distributed to Insider Channels.
Microsoft missed the bug despite users filing reports in its Feedback Hub, since the number of total reports of file deletion was too low to trigger a quicker response by its engineers.
Microsoft added code in the October 2018 update that would make sure these empty duplicate folders were removed.
In a blog post, the company says the number of customers impacted by the bug was small, with "reports of data loss" limited to "one one-hundredth of one percent of version 1809 installs". The root cause of this issue, as it turns out, is the "Known Folder Redirection" feature that when enabled, moved files from folders such as Documents, Pictures, Desktop, Camera Roll, Screenshots Videos etc.to a new folder, but was deleted from either folders due to some changes made to the logic from the feedback received from Insiders. For example, an empty copy of the original C:\Users\Name\Downloads folder appeared.
In response, Microsoft paused the OS rollout two days after the release of Windows 10 version 1809, Cable indicated.
Microsoft explains it has identified and fixed various scenarios in which KFR files were deleted, so you should no longer encounter the issue.
This includes fixes for system components such as the Windows kernel, graphics and file systems, the wireless networking and peripherals subsystems, along with the JET database engine, Windows Media Player and the Edge and Internet Explorer web browsers among others. Again, this is because there's a redirection, but old files remain in their default location, because OneDrive only used the redirect for autosave (for example, in a c:\users\username\onedrive\pictures folder).
The fixed versions of Windows are getting floated in Microsoft's Windows Insider Program, which is a program for software testers. If there are still files in the "Documents" folder then you're not affected by the issue, according to another tweet from Sarkar.
Microsoft has also changed the workaround text on its website.
For those who are affected, they should call Microsoft at +1-800-MICROSOFT or find a local number in your area.