Can you do grep rhys-pg10 /proc/*/mountinfo to see if anything is holding this mounted.
root@server01:~# grep rhys-pg10 /proc/*/mountinfo
/proc/12507/mountinfo:1450 578 0:191 / /var/snap/lxd/common/shmounts/storage-pools/lxd/containers/rhys-pg10 rw shared:248 - zfs lxd/containers/rhys-pg10 rw,xattr,posixacl
/proc/17834/mountinfo:4902 4993 0:191 / /var/snap/lxd/common/shmounts/storage-pools/lxd/containers/rhys-pg10 rw shared:248 - zfs lxd/containers/rhys-pg10 rw,xattr,posixacl
/proc/19416/mountinfo:4902 4993 0:191 / /var/snap/lxd/common/shmounts/storage-pools/lxd/containers/rhys-pg10 rw shared:248 - zfs lxd/containers/rhys-pg10 rw,xattr,posixacl
/proc/19691/mountinfo:4902 4993 0:191 / /var/snap/lxd/common/shmounts/storage-pools/lxd/containers/rhys-pg10 rw shared:248 - zfs lxd/containers/rhys-pg10 rw,xattr,posixacl
/proc/19699/mountinfo:4902 4993 0:191 / /var/snap/lxd/common/shmounts/storage-pools/lxd/containers/rhys-pg10 rw shared:248 - zfs lxd/containers/rhys-pg10 rw,xattr,posixacl
/proc/20004/mountinfo:4902 4993 0:191 / /var/snap/lxd/common/shmounts/storage-pools/lxd/containers/rhys-pg10 rw shared:248 - zfs lxd/containers/rhys-pg10 rw,xattr,posixacl
/proc/21227/mountinfo:1450 578 0:191 / /var/snap/lxd/common/shmounts/storage-pools/lxd/containers/rhys-pg10 rw shared:248 - zfs lxd/containers/rhys-pg10 rw,xattr,posixacl
/proc/24848/mountinfo:4902 4993 0:191 / /var/snap/lxd/common/shmounts/storage-pools/lxd/containers/rhys-pg10 rw shared:248 - zfs lxd/containers/rhys-pg10 rw,xattr,posixacl
/proc/32019/mountinfo:4902 4993 0:191 / /var/snap/lxd/common/shmounts/storage-pools/lxd/containers/rhys-pg10 rw shared:248 - zfs lxd/containers/rhys-pg10 rw,xattr,posixacl
/proc/3711/mountinfo:1450 578 0:191 / /var/snap/lxd/common/shmounts/storage-pools/lxd/containers/rhys-pg10 rw shared:248 - zfs lxd/containers/rhys-pg10 rw,xattr,posixacl
/proc/3944/mountinfo:1450 578 0:191 / /var/snap/lxd/common/shmounts/storage-pools/lxd/containers/rhys-pg10 rw shared:248 - zfs lxd/containers/rhys-pg10 rw,xattr,posixacl
/proc/4086/mountinfo:1450 578 0:191 / /var/snap/lxd/common/shmounts/storage-pools/lxd/containers/rhys-pg10 rw shared:248 - zfs lxd/containers/rhys-pg10 rw,xattr,posixacl
/proc/4930/mountinfo:1450 578 0:191 / /var/snap/lxd/common/shmounts/storage-pools/lxd/containers/rhys-pg10 rw shared:248 - zfs lxd/containers/rhys-pg10 rw,xattr,posixacl
/proc/5314/mountinfo:1450 578 0:191 / /var/snap/lxd/common/shmounts/storage-pools/lxd/containers/rhys-pg10 rw shared:248 - zfs lxd/containers/rhys-pg10 rw,xattr,posixacl
/proc/6228/mountinfo:1450 578 0:191 / /var/snap/lxd/common/shmounts/storage-pools/lxd/containers/rhys-pg10 rw shared:248 - zfs lxd/containers/rhys-pg10 rw,xattr,posixacl
/proc/6641/mountinfo:1450 578 0:191 / /var/snap/lxd/common/shmounts/storage-pools/lxd/containers/rhys-pg10 rw shared:248 - zfs lxd/containers/rhys-pg10 rw,xattr,posixacl
/proc/8018/mountinfo:1450 578 0:191 / /var/snap/lxd/common/shmounts/storage-pools/lxd/containers/rhys-pg10 rw shared:248 - zfs lxd/containers/rhys-pg10 rw,xattr,posixacl
/proc/8263/mountinfo:1450 578 0:191 / /var/snap/lxd/common/shmounts/storage-pools/lxd/containers/rhys-pg10 rw shared:248 - zfs lxd/containers/rhys-pg10 rw,xattr,posixacl
/proc/8392/mountinfo:4902 4993 0:191 / /var/snap/lxd/common/shmounts/storage-pools/lxd/containers/rhys-pg10 rw shared:248 - zfs lxd/containers/rhys-pg10 rw,xattr,posixacl
/proc/8911/mountinfo:1450 578 0:191 / /var/snap/lxd/common/shmounts/storage-pools/lxd/containers/rhys-pg10 rw shared:248 - zfs lxd/containers/rhys-pg10 rw,xattr,posixacl
grep: /proc/9013/mountinfo: Invalid argument
grep: /proc/9023/mountinfo: Invalid argument
grep: /proc/9024/mountinfo: Invalid argument
grep: /proc/9025/mountinfo: Invalid argument
grep: /proc/9028/mountinfo: Invalid argument
This is how I solved the issue. It’s still an open issue for this problem. I will repeat the instructions below on how I solved the issue it might help you too, give it a try.
lxc@lxdserver1:~$ lxc stop test1
lxc@lxdserver1:~$ lxc copy test1 test2
lxc@lxdserver1:~$ lxc delete test1
lxdserver | FAILED | rc=1 >>
Error: Failed to run: zfs destroy -r local/containers/test1: cannot destroy 'local/containers/test1': dataset is busynon-zero return code
lxc@lxdserver1:~$ sudo grep test1 /proc/*/mounts
/proc/3585/mounts:local/containers/test1 /var/snap/lxd/common/lxd/storage-pools/local/containers/test1 zfs rw,xattr,posixacl 0 0
lxc@lxdserver1:~$ ps aux | grep 3585
root 3585 0.0 0.0 234844 1412 ? Sl Feb17 0:00 lxcfs /var/snap/lxd/common/var/lib/lxcfs -p /var/snap/lxd/common/lxcfs.pid
lxc@lxdserver1:~$ sudo kill 3585
lxc@lxdserver1:~$ lxc delete test1
lxc@lxdserver1:~$
Thanks for you reply, but as all containers were working for clients and each container that had issues also contained many many /proc/ dependencies, i left it until the monthly patching and then rebooted and this fixed the issues. But i have issues again recently of the same type, different containers, all since a snap update/refresh.