Comment 89 for bug 736743

Robert Hardy (rhardy) wrote :

This same issue bit me using 18.04. I think this should really be reclassified as an installer bug.
Ubuntu has known for many releases that a single btrfs root partition does not work properly.
The installer should warn people when they use a single partition that is btrfs that grub cannot write to it and you may want a separate ext4 /boot partition to avoid problems.