John Cable, Director of Program Management, Windows Servicing and Delivery penned a long blog post to explain what went wrong during testing.
Security updates to Internet Explorer, Windows Media Player, Microsoft Graphics Component, Windows Peripherals, Windows Shell, Windows Kernel, Windows Datacenter Networking, Windows Storage and Filesystems, Microsoft Edge, Microsoft Scripting Engine, Windows Linux, and the Microsoft JET Database Engine.
#WindowsInsiders If you've run into the "missing files after update" issue for 1809/October 2018 Fall update, please call our support line. At the time the bug was discovered, the October 2018 Update was only being offered to users who had manually clicked the "Check for updates" button within Windows settings, which Microsoft credits with helping to minimize its impact.
Users who are affected by the issue are missing files and folders in their "Documents" folder.
The company points toward Windows 10's Known Folder Redirection (KFR) feature, which allows Windows folders (like Desktop, etc) to be redirected from their default locations to new locations. You create "D:\documents" and change the location of the files known folder from the original "old" location c:\users\username\documents to D:\documents. However, it is holding back on releasing the new operating system generally until further testing is completed. Microsoft made no mention of that in the update on the Windows Experience website. Microsoft is continuing to hold back not just Windows 10 version 1809, but also Windows 10 IoT and Windows Server 2019 to address the software flaws. Well, the good news is that the files can be recovered, however, Microsoft expects a phone call from you to do be able to do that. But we're shocked that Microsoft messed up in the first place. So that's a curious absence right there and at many other stores also. For more information, please refer to our Windows 10 update history page (KB article), which we are updating with new information as it is available. Previously the company only advised users to not install the update. It notes that Microsoft will provide a notice when the Windows 10 version 1809 rollout resumes.