My colleague Martin Geuss, Microsoft MVP, has already been pointed out in Dr.Windows, that you should not use  Windows 10 Preview in a production environment.

For testing you should also think about a separate Windows Account.

I have received a notice …

after upgrading from Windows 8.1 to Windows 10 Preview

… and this morning I went to open a personal document from consumer OneDrive… but the doc wasn’t there. Then I realised that a couple of folders were missing and in turn realised that thousands of my photos had disappeared.
Luckily, I located these thousands of files in the OneDrive recycle bin and have now restored them. But why did this even happen in the first place?
I think this is probably something to do with OneDrive wanting to make everything available offline after I’d upgraded (which I didn’t want), so I set everything to be available online-only (everything was already online prior to the u/g) and then I could later choose what I wanted to be offline. Although I don’t really know why this resulted in so many files being moved to the OneDrive recycle bin.
I think everything is now back to "normal"…

The background should (could) be under circumstances that OneDrive is a newer Version in Windows 10 Preview

Windows 8.1	Windows 10 Preview
Version 6.3.9600.17278	Version 6.4.9841.0

So we see that the minor version is increased from 3 to 4.
You always should noticed:

"Windows 10 is a preview is a preview is a preview"