Microsoft MVP Reminds that Backups are Necessary After Windows 10 1809 Upgrade Deletes User’s Files
 
https://myitforum.com/microsoft-mvp-reminds-that-backups-are-necessary-after-windows-10-1809-upgrade-deletes-users-files/
 
The article states: Be careful out there. More bugs for Windows 10 1809 are being reported by the hour.

So 1809 is like ransomware, but without the option to pay ransom.

I've upgraded my desktop and a 2017 model Dell Inspiron 15 laptop.  Only one problem, on the desktop the default audio playback device and recording device was reset.  I had to manually set my "Speakers" (PC sound card) to the default audio playback device and "Stereo Mix" to the default recording device.  
 
A couple of plug-ins had to be reauthorized but that always happens on a major update such as this so I don't consider that a "problem".
 
There are always some that have problems of one thing or another on an upgrade and some of these are "self inflicted".  Murphy's Law applies too.
 

I'm still on 1803 from June. What's been updated in 1809?
 
According to the article, files in My Document folders seem to be deleted. If so you can run a recovery program to get them back.
 
As a side point, I never use default Windows folders for documents of any type. My files are on another hard drive in folders of my own making where Windows can't (better not) touch them.
 
We'll see.

As more users fall victim to this known bug (deleting user files), though still not acknowledged by Microsoft, one cause has now been found (registry). Also, Woody Leonard posts a possible way to get your files back.
 
Here is the latest:
 
https://myitforum.com/the-cause-for-windows-10-1809-upgrades-deleting-user-files/

To add, nothing was deleted in my Documents folder.  
 

My desktop PC's upgraded without issue, well, apart from having to upgrade to the latest beta drivers for my 1st gen focusrite scarlett 6i6 & 18i20, and the usual XLN re-authorisation.
 
My laptop however, refuses to upgrade. It goes all the way to the end, I restart, it gets to 9% then does a rollback. That's both using Windows update (for which 1809 no longer appears), and using the Windows Upgrade Assistant.
 
What gets me, is that it doesn't give me any indication as to why it rolled back.
 
I guess it's time to do a fresh install at some point, but it'll have to wait... 

V1809, Build 17763.1 has been pulled by MS.  No specific reason but the problem some are having with deleted files may be one reason.  I've had 17763.1 for over a week as I get the advanced "Insider" versions and didn't have problems with it either.  Not sure of what circumstance(s) cause the problems.  
 
But, I'll repeat the suggestion (really should be mandatory) to make a full drive (all partitions) image backup to a separate drive BEFORE doing any major update such as this.  The free (and most popular on computer forums I visit) Macrium Reflect or some other imaging program should be used to make the disc image.  DO NOT use the built in Windows backup as its incomplete and does not do a full backup.
 
Macrium Reflect free:
 https://www.macrium.com/reflectfree

fireberd
V1809, Build 17763.1 has been pulled by MS.  No specific reason but the problem some are having with deleted files may be one reason.  I've had 17763.1 for over a week as I get the advanced "Insider" versions and didn't have problems with it either.  Not sure of what circumstance(s) cause the problems.  
 
But, I'll repeat the suggestion (really should be mandatory) to make a full drive (all partitions) image backup to a separate drive BEFORE doing any major update such as this.  The free (and most popular on computer forums I visit) Macrium Reflect or some other imaging program should be used to make the disc image.  DO NOT use the built in Windows backup as its incomplete and does not do a full backup.
 
Macrium Reflect free:
 https://www.macrium.com/reflectfree

Yeah, I did an image of both my laptop drives with clonezilla before I started! Thankfully I didn't need to use it, as the rollback succeeded.

msmcleod
My desktop PC's upgraded without issue, well, apart from having to upgrade to the latest beta drivers for my 1st gen focusrite scarlett 6i6 & 18i20, and the usual XLN re-authorisation.
 
My laptop however, refuses to upgrade. It goes all the way to the end, I restart, it gets to 9% then does a rollback. That's both using Windows update (for which 1809 no longer appears), and using the Windows Upgrade Assistant.
 
What gets me, is that it doesn't give me any indication as to why it rolled back.
 
I guess it's time to do a fresh install at some point, but it'll have to wait... 

I seem to recall reading about this (not necessarily your issue) in the forums yesterday, that even Microsoft will not upgrade certain pcs if it finds certain things (I didn't read carefully), I think one is an Intel issue, because it knows it will trash the pc. So maybe it encounters one of those issues and then quits and just rollsback? Just a thought, I really have no idea...