https://www.bleepingcomputer.com/news/microsoft/fixed-windows-10-october-2018-update-released-to-insiders-for-testing/

Today, Microsoft is releasing a fixed version of the Windows 10 October 2018 Update to Windows Insiders for the critical deletion bug. In a blog post, Microsoft's John Cable, Director of Program Management, Windows Servicing and Delivery confirmed that the bug that caused the removal of files on the certain system has been addressed and Windows 10 October 2018 Update is once again available to the Insiders.

Microsoft says that they have analyzed all reports of data loss and conducted an internal investigation to find out the cause of the files removal. 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.