Urbackup changes your root device to a DM device of its own creation, even after uninstalling, here are the offending lines:
/usr/share/initramfs-tools/scripts/local-top/urbackup-setup-snapshot:34:echo "0 $RBD_SIZE linear $RBD 0" | dmsetup create root-98d1f8b1f435 2> /dev/kmsg /usr/share/initramfs-tools/scripts/local-top/urbackup-setup-snapshot:36:echo "export ROOT=/dev/mapper/root-98d1f8b1f435" > /conf/param.conf
This had me going crazy. I couldn’t for the life of me figure out what was changing my root device mid-boot. It kept coming back after I removed the offending lines in the initrd and other boot scripts. I had to grep my whole boot volume looking for it. Especially confusing since I uninstalled the urbackup client from this computer months ago. This screws up the ubuntu update-grup script which sets the root volume in grub.cfg to the mapped volume, that doesn’t get mapped till after root is mounted, which causes boot to fail.
Edit: This was on Ubuntu 19.04