SOLVED installation of WIN10 update 1806 with install of 1903 after disabling all Intel virtualization features in BIOS.
My ASUS P6 motherboard based desktop would complete the v1806 update, but not reboot to a desktop. It would complete 100% and reboot but fail on the reboot. Alternatively, I tried to install the August 2019 1903 update. Neither the USB or DVD with the 1903 iso file would boot. I tried everything I could think of and followed hunfreds of suggestions to install the updates. Nothing worked. The desktop would always fail to launch the desktop after reboot and would revert back to its prior version. Finally, I went into the BIOS and disabled two setting related to Intel Virtualization. Once Intel Virtualization was disabled. I was able to easily install the 1903 update from an ISO I had copied to the desktop. The update installed smoothly and rebooted as it should. ALL IS WELL in updaate land for now.
This worked for me, I'm now running 1903.