After installing nVidia drivers, the machine boots to a initramfs prompt in kernel 4.13. 4.10 boots fine, although the x server crashes continuously. In 4.13 initramfs, dmesg reveals that there was an error mounting the root fs. btrfs check reports that the fs is fine, but mounting it manually gives the same result. It's using btrfs raid 1. Mounting the second copy works fine, and after that mounting the first one works as well. The only way I can make the system bootable again is to remove the nVidia drivers.
ProblemType: Bug
DistroRelease: Ubuntu 17.10
Package: nvidia-384 384.90-0ubuntu3
ProcVersionSignature: Ubuntu 4.10.0-38.42-generic 4.10.17
Uname: Linux 4.10.0-38-generic x86_64
ApportVersion: 2.20.7-0ubuntu3.1
Architecture: amd64
Date: Sun Nov 5 12:23:17 2017
InstallationDate: Installed on 2016-03-25 (590 days ago)
InstallationMedia: Ubuntu 15.10 "Wily Werewolf" - Release amd64 (20151021)
SourcePackage: nvidia-graphics-drivers-384
UpgradeStatus: Upgraded to artful on 2017-10-31 (5 days ago)
Tried changing the grub command line to boot from the other disk of the raid set. It gave me the same error on that disk, but the one I was using previously was mountable.
Also, checked SMART data for signs of disk failure, but everything looks fine.