It looks like the LXD snap has mounted "proc" and "sys" over /var/snap/lxd/common/var/lib/lxcfs/{proc,sys}/ but it's not unmounting them.
In the "remove" hook, the LXD snap should unmount any mounted filesystems; not doing so can have disastrous effects if there are also user partitions mounted in there.
It looks like the LXD snap has mounted "proc" and "sys" over /var/snap/ lxd/common/ var/lib/ lxcfs/{ proc,sys} / but it's not unmounting them.
In the "remove" hook, the LXD snap should unmount any mounted filesystems; not doing so can have disastrous effects if there are also user partitions mounted in there.