FWIW snapd mounts and unmounts a squashfs on startup to determine whether the system can mount squashfs's. It does this using mount, and cleans up with umount -l. That is, it's not via systemd in this instance in particular.
I'm setting it as invalid for snapd, but if this behaviour is somehow tickling a bug and there's a workaround that could avoid it, let us know and we'd be happy to accommodate (set the bug task back to New so our triage picks it up).
FWIW snapd mounts and unmounts a squashfs on startup to determine whether the system can mount squashfs's. It does this using mount, and cleans up with umount -l. That is, it's not via systemd in this instance in particular.
I'm setting it as invalid for snapd, but if this behaviour is somehow tickling a bug and there's a workaround that could avoid it, let us know and we'd be happy to accommodate (set the bug task back to New so our triage picks it up).