Lookup the container who runs this process

grep -rn pid /sys/fs/cgroup/pids/*

Error: The ‘default’ profile cannot be deleted

printf 'config: {}\ndevices: {}' | lxc profile edit default

Existing Parition, create new lvm storage pool

pvcreate /dev/sda2
lxc storage create myPool lvm source=/dev/sda2 lvm.thinpool_name=myPool

lxc network create vmbr03
Error: Unable to kill dnsmasq: Could not kill process: os: process not initialized

In my case, the network did not appear when I ran lxc network list.
Check /var/snap/lxd/common/lxd/networks and delete the network

rm -r vmbr03
lxc network create vmbr03
Network vmbr03 created

This machine ID is already enabled with a different key or is non-unique.

Or

error executing enable: cannot enable machine: bad temporary server status 500

Likely you installed your VM with a template and the machine ID is not unique.
But you can easy fix that.

rm -f /etc/machine-id
dbus-uuidgen --ensure=/etc/machine-id
rm /var/lib/dbus/machine-id
dbus-uuidgen --ensure

You need to reboot afterwards.
Warning: Some people say it might fuck up things.
So far it worked fine even on running LXD nodes (no clusters tested).