Zfs Mount giving no mountpoint set on some containers

I do a very simple backup of files in a container via mounting the container and copying file to another drive. It works pretty fast. But Some containers give this error.
cannot mount ‘local/containers/WP-TWOTIGERS’: no mountpoint set

Anyone know why? Thanks

See bash below.

zfs mount local/containers/$1
rsync -vrz /var/snap/lxd/common/lxd/storage-pools/local/containers/$1/rootfs/var/ /mnt/md0/backup/$1