According to Microsoft, a very small number of users lost files after installing Windows 10 October 2018 Update and it occurred on systems that had Known Folder Redirection (KFR) enabled, but files remained in the original "old" folder location vs being moved to the new, redirected location.
For everyone else, the updated October 2018 version has been released to Windows Insiders, who can now install and test it out. "We will carefully study the results, feedback, and diagnostic data from our Insiders before taking additional steps towards re-releasing more broadly", Cable said. Anyone who is still missing data after installing the original update can contact Microsoft support or go to one of its retail stores where they can attempt to recover lost files.
"We have fully investigated all reports of data loss, identified and fixed all known issues in the update, and conducted internal validation", Microsoft said in the blog post.
Microsoft made a decision to remove these duplicate folders through code incorporated into version 1809. While the reports of actual data loss are few (one one-hundredth of one per cent of version 1809 installs), any data loss is serious.
Users who moved a Known Folder to OneDrive but did not move files in the process had files deleted in the old location.
The bug, Cable wrote, affected people who had used a feature called Known Folder Redirection, a tool for folks who have filled their hard drive and wanted new files destined for their Desktop, Documents, Pictures, Videos, Camera Roll, and other such default directories to be stored on another device, such as in D:\user.
Quietly, Microsoft took the opportunity to fix a bug that saw user profiles being deleted due to an incorrect timing calculation. "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".
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. If KFR had been previously enabled, intentionally or by mistake/automatically, but the files remained in the old location instead of being moved to the redirected location, they ended up being deleted. To make sure to remedy such issues, the Windows Insider team says that it is adding the ability to flag the severity of the feedback that they initiate.
If you did experience data loss, Microsoft Support advises you call +1-800-MICROSOFT for help.