I could reproduce. It works when you login as Nextcloud admin but it doesn’t work when logged in as Domain user, even if she has admin rights…could be a bug.
I think the best way to map user home shares is to add them to the personal external storage of the user.
AFAIK it just removes the share from Nextcloud without deleting the data in the samba share.
EDIT:
Yes, I think it works without restart of Nextcloud when done via occ files_external:import