Update: Nov. 8, 8:10 p.m. ET: Microsoft sent a statement saying this issue will soon be fixed for users automatically:
“A limited number of customers experienced an activation issue that our engineers have now addressed. Affected customers will see resolution over the next 24 hours as the solution is applied automatically. In the meantime, they can continue to use Windows 10 Pro as usual.” – Jeff Jones, senior director, Microsoft
The company also said that watermarks will disappear once the fix is applied. The original story is below:
Microsoft's had a rough month. The company attempted to release the Windows 10 October 2018 Update during its namesake month only to pull it after numerous file system bugs were discovered; it still has yet to be re-released to the public. Now several Redditors have reported that their Windows 10 Pro licenses have been mysteriously deactivated, with their systems prompting them to install Windows 10 Home instead. Windowsunited.de was among the first to report on the issue.
It's not clear what's causing this issue. Numerous people said their Windows 10 Pro license was carried over from Windows 8, so it could be related to that migration, though it's strange to encounter problems like this so long after Windows 10 debuted. Several members of the Windows Insider Program who tested Windows 10 Pro before its release have also had this problem, which could mean the migration path isn't at fault.
Update, Nov. 8, 3:36 p.m.: "We’re working to restore product activations for the limited number of affected Windows 10 Pro customers." said Jeff Jones, a senior director at Microsoft.
Things got even weirder after the original poster said they restarted their system only to find that their license now claimed to be for Windows 10 Enterprise for Virtual Desktops. At this point it almost seems like Windows 10 is flicking a spinner whenever the system is restarted, noting the result, and then saying the license is for whatever version of Windows 10 it landed on. That's not what people want from their operating system.
We haven't experienced this problem ourselves, and like always, the warnings about online complaints apply here. The vast majority of Windows 10 Pro license owners probably haven't been affected by this problem.