Maybe others have already replied with the same thing. What happened to me was that the entire C:\Users<profile>\Documents folder was moved to OneDrive.
Before the October update I had files stored in the local Documents folder, mostly different kind of log files. After the update all files have been moved to C:\Users<profile>\OneDrive\Documents leaving the local Documents folder empty.
If you haven't checked already, you should have a look at your OneDrive regardless if you actually use it or not.