https://arstechnica.com/gadgets/2018/10/microsoft-suspends-distribution-of-latest-windows-10-update-over-data-loss-bug/

Earlier this week, Microsoft started distributing the Windows 10 October 2018 Update, version 1809, to Windows users who manually checked for updates. The company has now halted that rollout after many reports that installing the update is causing serious data loss: specifically, deleting the Documents, and perhaps Pictures, folders. Microsoft is also advising anyone who has downloaded the update but not yet installed it to not install it at all.

The exact circumstances causing data loss aren't clear; the handful of reports on Microsoft's forums and Reddit don't have any obvious commonalities, and people report seeing only one affected system among many when upgraded. There will need to be some amount of investigation before a fix can be developed.