Thank you Seth for sharing.
I had the exact same problem with an Asus Zenbook Pro while Windows was trying and failing to install that 1803 update.
Updating the Bios magically fixed this.
I wonder how many Asus owners are going to be impacted by this really REALLY bad update experience...
Windows 10 team: please fix this asap, and consider adding some extra test cases for future updates so this doesn't happen again. Thank you.