It’s normal that you don’t see things mounted under /var/snap/lxd/common.
Snaps operate in a separate mount namespace so they don’t disturb the host.
You can inspect things through /var/snap/lxd/common/ns/var/snap/lxd/comon/lxd/storage-pools/... if you need to.
lxc storage show when clustered does not show host-specific options like source, for that you need to specify --target with the name of one of the cluster members.
As for the actual shifting issue, that’s most often caused by the number of ACL entries having increased to a point where we can’t add more. There was a bug causing that in much older LXD, so that may be the source of this issue.
Easiest workaround in this case would likely be to blow away that directory unless you expect to need access to older journal entries for this container.