Windows 10 version 1809, build 17763, will delete some user account folders if they are in the default location and not synced to OneDrive.
If user account files such as Documents, Music, Photos and Downloads are stored in their default location and they are not getting synched with OneDrive, you may notice some or many missing files in those folders on Windows 10 after applying the update to version 1809.
Microsoft has halted the rollout of Windows 10 version 1809 and the current recommendation is to backup anything important in the user account location folders and DO NOT manually apply the update.
The link below has more information about this issue:
The links below contain more information about Microsoft's halting of the update rollout.
We are closely monitoring the situation and this document will be updated with further recommendations as more information becomes available.