Well my migration didn't go well either. After running the migration command I lost all my machines...(lxc list shows no machines) I was using ZFS as a storage backend, but it looks like the migration failed to move the ZFS to the newly installed LXD version.
I noticed these errors:
error: Unable to connect to the source LXD: Get http://unix.socket/1.0: dial unix /var/lib/lxd/unix.socket: connect: no such file or directory
The migration process will shut down all your containers then move your data to the destination LXD.
Once the data is moved, the destination LXD will start and apply any needed updates.
And finally your containers will be brought back to their previous state, completing the migration.
Are you ready to proceed (yes/no) [default=no]? yes
=> Shutting down the source LXD
=> Stopping the source LXD units
=> Stopping the destination LXD unit
=> Unmounting source LXD paths
=> Unmounting destination LXD paths
=> Wiping destination LXD clean
=> Moving the data
=> Moving the database
=> Backing up the database
=> Opening the database
=> Updating the storage backends
error: Failed to update the storage pools: Failed to run: zfs list -H -t all -o name,mountpoint -r : cannot open '': invalid dataset name