Shortly after the October 2018 Update became available, users began reporting that the upgrade appeared to be deleting files. According to a new post from Microsoft, the issue only affected "one one-hundredth of one percent of version 1809 installs," but it was still a large enough problem to cause the update to be pulled.
Microsoft is working to re-release the October 2018 Update publicly, but it is first testing a new build that it says fixes the file deletion issue. Windows Insiders can get their hands on the updated release starting today, and Microsoft says it will "carefully study the results, feedback, and diagnostic data" from Insiders before continuing the public rollout.
As for the issue itself, Microsoft has filled in some of the technical details concerning what caused the files to go missing:
In previous feedback from the Windows 10 April 2018 Update, users with [Known Folder Redirect] reported an extra, empty copy of Known Folders on their device. Based on feedback from users, we introduced code in the October 2018 Update to remove these empty, duplicate known folders. That change, combined with another change to the update construction sequence, resulted in the deletion of the original "old" folder locations and their content, leaving only the new "active" folder intact.
Correcting the issue required three specific fixes, each of which you can read about in more detail in Microsoft's blog post.
For those who have already been impacted by the issue, Microsoft continues to recommend you contact their support line or bring your PC into a nearby Microsoft Store for servicing.
Though the problem may have affected a relatively low number of users, the result was a gut punch to Microsoft's current update process. Going forward, the company has added a new feature to the Windows Insider Feedback Hub, through which users can flag issues by their impact and severity. "We expect this will allow us to better monitor the most impactful issues even when feedback volume is low," Microsoft says.
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