windows 10 (October 2018 update) (version 1809) deleted all my files

Yes. In between my last post and this Bulldog explained the source of the issue on another thread. Sure glad I never used File Redirection as even with backups reinstalling can be time consuming as all get out.

Still...better then never backing up.

That's right about making backups. Here is the official MSFT explanation...

https://blogs.windows.com/windowsexperience/2018/10/09/updated-version-of-windows-10-october-2018-update-released-to-windows-insiders/#yRlroHtaQVHofZu3.97

Updated version of Windows 10 October 2018 Update released to Windows Insiders

It's an issue of Known Folder Redirection (KFR). C**:\users<Username>** is normally where the "known" user folders are kept, like Desktop, Documents, etc. But they can be moved elsewhere, like to OneDrive or to another HDD. Many did redirect them prior to the 1809 upgrade. After redirection (no matter to where), if files were left behind (or subsequently added to) the known folder (i.e., the original location) - they got deleted by the 1809 update.

That's the sad story. I was spared because my redirections left nothing behind. The size of files & the capacity of OneDrive had nothing to do with it. They weren't being moved - just plain deleted. Excellent to have backups.

This is not a general issue. I didn't lose any files when I updated to Windows 10 version 1809 on October 4th nor from any of the updates that have been issued since:

Now I am using an HP Desktop PC 510-p009 64 bit.

I do NOT have OneDrive installed. I don't LIKE OneDrive (as an automatic process, I mean).

Now it would be interesting to learn what those who lost files have in common (e. g. make, model, make of Processor, whether or not they have OneDrive installed) etc.

I can suggest that if the issue involves the Update MOVING all a user's files to OneDrive during the Upgrade (I cannot imagine WHY it would do that but some users have said that that was where they found their missing files) it would matter VERY much how much storage one had available on OneDrive. The storage limit for their Basic Plan (free) is 5GB.

So any files OVER that size would be deleted, one assumes. At any rate, they would not be uploaded and unless the computer had additional instructions from the OneDrive part to leave them where they were they might just get deleted.

Now IF this (or something like this) happened Microsoft would have no copies of your files and any recovery software would do as well as anything they might propose in the future. 

And again, as most of you were no doubt told in your computer classes in school BACK UP YOUR FILES. I know, that doesn't help now but, seriously, there was a reason your teachers brought that up.

This is that reason: "If anything CAN go wrong, it will."

And, finally, install WUSHOWHIDE to help you in avoiding further Updating issues.

For Get Data Back I run it on another system with the drive attached via a dock. We do this on one of our "servers" at the repair shop I work at. There's also a company called Ease US that makes some decent recovery software as well you could try out. Many of their software comes in a bootable format as well.