Heads-Up! Multiple reports of the April 2017 Rollup Packages causing Windows Server 2016 or Windows 10 to fail to boot with "INACCESSIBLE_BOOT_DEVICE". I've seen it on one of my own Win2016 servers running under VMWare ESXi 6.
I'm still waiting on "Working on updates" now, but I was at least able to get past the initial boot failure by booting in to Windows PE and using DISM to uninstall the packages, as described at https://www.tecklyfe.com/windows-kb4015217-windows-server-2016-windows-10-vmware-inaccessible-boot-disk/
Boot into Windows 2016 (or Windows 10) ISO.
Go to Repair
Go to Tools to get a command prompt.
Confirm the drive letter for the Windows image. Usually D: –> dir d:
Run the following to view the installed packages which will also show a date of install.
Dism /Image:D:\ /Get-Packages
Find the package(s) that were just installed by date. Run the following command on each package:
example: dism.exe /image:d:\ /remove-package /packagename:Package_for_KB4014329~31bf3856ad364e35~amd64~~10.0.1.0
My server had a different packagename (based on Package_for_Rollup~31bf3856ad364e35~amd64~~ with a version number), but the output of "/Get-Packages" shows installation date so it should be pretty easy to deduce which package is at fault.
edit: I'm back to the desktop now, successful rollback