Yes - the problem seems to be that at boot time the ExecStart=/usr/lib/samba/samba-config initiated from samba-config.service failes to create (or create in time ??) the /run/samba/smbpasswd that smbd is looking for during startsmbfilepwent_internal , so smbd recreates an empty smbpasswd file.
Executing /usr/lib/samba/samba-config later in an SSH session *does* create a proper /run/samba/smbpasswd
So, my question is ... how do I ensure that a populated smbpasswd file is created and|or created in time for smbd to find ?