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. This is the feature that lets you move a known folder like C:\Users\Name\Downloads to D:\Downloads, for example.
"We have paused the rollout of the Windows 10 October 2018 Update (version 1809) for all users as we investigate isolated reports of users missing some files after updating", Microsoft writes. Some issues included minor task manager bugs, but a showstopper bug that was deleting user files meant that the company had to pull the update out of distribution completely.
Doing what they should have done a week ago, before RTM, Microsoft has released a new build of the Windows 10 October 2018 update to Windows 10 Insiders in the Slow Ring and Release Preview Ring. If there are still files in the "Documents" folder then you're not affected by the issue, according to another tweet from Sarkar.
In an official blog post, the tech giant has stated that only a small number of Windows users were affected by the problem - specifically, less than one one-hundredth of 1% (or 0.0001%) of all installs.
Known Folder Redirects gives users options to move the classic Windows folders Desktop, Documents, Pictures, Videos, and so on to another location.
Implementation of code to remove empty duplicate known folders automatically during upgrade.
Based on that statement, it appears that the deleted files may be recoverable, but it's definitely a good idea to refrain from using the computer further to ensure that things don't get overwritten and lost forever. "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 would allow Microsoft to monitor both critical issues and features suggestions. 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.