Unable to delete shared folder

I'm having problems deleting a share, quite likely because I've done something stupid. I had been trying to delete a directory from a terminal, forgetting that I had created an SMB share for it. Having realised, I deleted the SMB share which enabled the delete button on the Shared Folder itself. That appeared to work but applying the changes resulted in:

Failed to execute command 'export PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin; export LANG=C; systemctl disable 'sharedfolders-WindowsBackupSets.mount' 2>&1' with exit code '1': Failed to disable unit: No such file or directory

I found a recent thread with a similar error message. Posts in there talked about editing config.xml but I wasn't sure that the symptoms were quite the same (my error occurs when I try to apply changes, not when I hit the delete button on the share) so I thought I'd better seek advice from folk who know what they're doing. I'm quite new to OMV and not exactly a whizz with Linux generally so I don't want to risk fiddling any further in case I just dig myself a deeper hole...

That's what I thought, and had I tried recreating the directory (under /srv/dev-disk-by-label-<label>/) without success. I read a comment in another thread about the entries under /sharedfolders/ being "bind mounts" of the main mounts under /srv/ so I tried recreating that too, but also without success. That's when I decided to accept that I was out of my depth. However...

I had to reboot recently the host this afternoon (my OMV installation is on a VM under ESXi, in case that's relevant) and another attempt has now produced a different error message relating to a separate share. Unlike the other share, I don't think I've interfered with this one:

Failed to execute command 'export PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin; export LANG=C; systemctl restart 'sharedfolders-Backups.mount' 2>&1' with exit code '1': Job for sharedfolders-Backups.mount failed. See "systemctl status sharedfolders-Backups.mount" and "journalctl -xe" for details.

This error is evidently on attempted service restart rather than disable, and there was no reference to a Job in the other message I copied. The directory mentioned in this error (Backups) exists both under /srv/dev-disk-by-label and under /sharedfolders/

systemctl status sharedfolders-Backups.mount (as root) produces:

● sharedfolders-Backups.mount - Mount shared folder Backups to /sharedfolders/Backups
Loaded: loaded (/etc/systemd/system/sharedfolders-Backups.mount; enabled; vendor preset: enabled)
Active: active (mounted) (Result: exit-code) since Wed 2018-11-14 14:16:50 GMT; 24min ago
Where: /sharedfolders/Backups
What: /dev/sdb1
Process: 15304 ExecUnmount=/bin/umount /sharedfolders/Backups (code=exited, status=32)
Tasks: 0 (limit: 4915)
CGroup: /system.slice/sharedfolders-Backups.mount

Nov 14 13:38:17 omv systemd[1]: Mounting Mount shared folder Backups to /sharedfolders/Backups...
Nov 14 13:38:17 omv systemd[1]: Mounted Mount shared folder Backups to /sharedfolders/Backups.
Nov 14 14:16:50 omv systemd[1]: Unmounting Mount shared folder Backups to /sharedfolders/Backups...
Nov 14 14:16:50 omv systemd[1]: sharedfolders-Backups.mount: Mount process exited, code=exited status=32
Nov 14 14:16:50 omv systemd[1]: Failed unmounting Mount shared folder Backups to /sharedfolders/Backups.

I don't know whether this is a step forwards or just sideways.