Windows 10 October 2018 update may delete your files during upgrades
https://www.cnet.com/news/windows-10-october-2018-update-may-delete-personal-files-during-some-upgrades/
It's not happening to all users, but no one seems to have isolated the cause of the issue yet. We've reached out to MIcrosoft for clarification, but did not immediately hear back.