Looking at https://github.com/lxc/lxd/issues/4504#issuecomment-384759354, it seems that the system may not have had ubuntu-standard installed, so on do-release-upgrade the final package removal step may have listed apparmor.
Looking at https:/ /github. com/lxc/ lxd/issues/ 4504#issuecomme nt-384759354, it seems that the system may not have had ubuntu-standard installed, so on do-release-upgrade the final package removal step may have listed apparmor.