Fault: on a very few occasions after a windows update, an AzureAD (pc is AzureAD joined)account, *I think the one that was logged in at the start of the update process*, after login will come up to a black screen with a mouse pointer, however the GUI does not respond to clicks.
Ctrl-Alt-Del will bring up the security screen fine, can open task manager and log out OK and the login screen shows up. With the problem account, after a bit of button pressing I can hit the Win key to pull up the start menu (which appears to work fine), and peek preview will allow me to see the wallpaper, any programs i start, and desktop icons fine, but once i try to select any active window, or the desktop the screen goes back to black with pointer. This only happens on the one specific account and any other logins are unaffected (both previously logged in accounts, and first time log ons).
I can recreate the situation on a windows 10 AzureAD joined machine (at least the several i tried): This is done manually via reg-edit removing the profile's UID in ProfileList, and the deleting the user profile directory. The next time that account ties to log on, you get the black screen with working start and "hidden" desktop as described above.
Troubleshooting: So we've ruled out graphics issues, it isn't the Win+P issue that was a thing during the insider previews pre-RTM, it appears to just be localized to AzureAD profiles (non administrator) that have been on the PC before and were logged in when one of the updates were applied and the PC restarts. Again this has only happened in less than 1% of updates across your networks (4 out of about 400).
The only way we can find to get past it is to do a soft or hard Windows reset and start from scratch. Obviously this turns a 15-20 minute profile reset into a 3 hour ordeal involving shipping the laptop back to this office.
And to sum up further details than I've described above:
Multiple hardware specs (Dell, Lenovo, HP) All fully up to date Win 10 All on AzureAD domains with PIN requirements Other local and AzureAD accounts work fine