I haven't been able to complete the 1803 update install either. After running Windows update and installing, the VM restarts and counts up the percentage installed as normal. Then it reboots again and shows the update progress again, but it stays at 0%, and the spinner doesn't move. There is hard drive and CPU activity for awhile, but after about a half hour, the both drop off and the VM is completely inactive. I've left it overnight twice now, and it never goes further.
After a reset, it gives me the option to roll back, but that just leads to a black screen. Fortunately I made a snapshot before rebooting to start the install, so I can at least get back into the system. But the snapshot was made after the update was downloaded, so it will try again on the next restart. Hopefully there's a solution to this issue soon, as I can't just keep rolling back to the old snapshot.
I have exactly the same issue - has someone an idea how to fix this?