Microsoft released the Windows 10 October 2018 update on the 3rd October, and I installed on the 4th. After which I noted a few odd behaviors, mainly that login to Store and Xbox completely failed to work for all users on all the upgraded computers. But I expected it would resolve itself in some upcoming bugfix and since I mainly use Steam rather than Xbox it was no big issue.
But after a few days of not being resolved I also started noting another problem, several of my applications wanted a repair or reinstallation. And after some investigation it turned out these are the non-cloud-aware applications that write directly to C:\Users\<username>\Documents rather than using the userprofile settings for where the Documents library currently resides, which is in OneDrive.
After which I discovered that for all upgraded computers and for all users who had logged in to these, the …\Documents, …\Pictures, and often but not always …\Music folders had been wiped of content. Which again, since mainly using OneDrive, did not become a the kind of critical issue it could have been a year ago. Now it was mostly game settings and highscores for the kids that got wiped out, at least as far as I can remember, and a few apps resynced from their clouds, or asked for a repair.
But it was still annoying, three isses are a few too many, and when I subsequently noted that Microsoft had withdrawn the October update I decided to rollback. Which went kind of ok, except instead of emptying the Documents, Pictures and Music, the rollback now completely deleted the entire folders. Again, mainly complaints from some applications and no real dataloss (since everything in them had already been lost).
So I manually re-created the folders and currently everything seems to run as it should again. Xbox and Store logins were automatically working once I had downgraded.
All in all an effective reminder of the importance of offline backup, not relying only on realtime cloud-synchronized data which could very well have been the case here.
One more minor glitch, which I can’t verify whether it related to the upgrade or not. When using family accounts, Microsoft automatically generates usage reports for childrens accounts and emails these to parents. For the days the computers were upgraded the report says the kids played for over 11 hours per day, (while the normal usage is more in the range of 0,5-2 hours). This is the first time the totals for the report has been inaccurate in this way, but it happened the same days and so the upgrade is my prime suspect.