Update 8/10/2018. Microsoft has halted the worldwide rollout of the Windows 10 v1809 upgrade until this problem is addressed.
There have been some reports that the latest Windows 10 upgrade to version 1809 has been deleting user data such as documents, photos etc.
It is critical to back up all files before any Windows 10 upgrade, but especially now.
An Image Backup is ideal.
For problem reports see: