Hi,
I realise this is an old thread, however I wanted to post in case it helps someone. Jenny Feng's answer should not be the accepted answer. I have included some additional pieces of advise in addition to the black screen problem during UWF maintenance.
- The black screen issue reported here by Steve West. I have been able to replicate the issue, and from what I can see it only happens if you reset the password for the UWF-Servicing account. In a working environment there is no need to set the password for this account as its managed entirely by Windows and the UWF feature. Providing you do not manipulate the 'UWF-Servicing' local Windows user account or reset the password, you should be able to run the 'uwfmgr servicing enable' command to successfully complete the maintenance. Key takeaway, don't reset this password!
- Another common problem you may encounter is the Screensaver not showing up/or the maintenance window never completing!!! (which is why some of you may go down the rabbit hole of resetting the 'UWF-Servicing' password so you can login to see whats happening (Don't do that!!) You need to manually take ownership of c:\windows\system32\UwfServicingMasterScript.cmd and update the file as per the Microsoft article. https://learn.microsoft.com/en-us/windows/iot/iot-enterprise/customize/uwf-master-servicing-script. When you install the UWF Windows feature 'DISM.exe /Online /enable-Feature /all /FeatureName:client-UnifiedWriteFilter', the UwfServicingMasterScript.cmd file is actually outdated and includes some incompatible commands. Thank you to this thread for point this out to me: https://superuser.com/questions/1078646/unified-write-filter-servicing-on-windows-10-enterprise-not-working-as-expected
- Further to the above, the screen saver still doesn't appear until you actually push this reg key to the machine. The article says its to change the default settings for the UWF maintenance screen saver, however if you dont write the keys... the screen saver doesnt appear at all. I suggest deleting the ColorBackground, ColorText and ColorProgress lines, as they create some pretty awful colors if you try and change those. https://learn.microsoft.com/de-de/windows/iot/iot-enterprise/customize/uwf-servicing-screen-saver
With the above changes, it all seems to work quite well and the Windows updates get applied.
It would be great if Microsoft fixed some of these issues or at least updated the documentation to reflect these workaround.