Have you compared the smb.conf files from the new server and one that's working?
Yeah. That was one of my side by side comparisons. First the GUI and then smb.conf
While I'm convinced there is a reason, or at least a workaround, this is something truly weird. I even went to the shared folder with WinSCP and applied the 777 mask - where everyone gets write (you do that by right clicking on the folder and properties). Still nothing. It's not a permissions issue. From what I can see with smbstatus, side by side with something that works, it's as if the samba service is running but the client is not connecting with the samba share VIA the designated network sockets.
Then there's this entry in a client log file, that crops up once in awhile;
chdir (/srv/dev-disk-by-label-WD1TB/ServerFolders/Backups) failed, reason: No such file or directory
smbXsrv_tcon_disconnect(0x9cd58d3d, 'Backups'): set_current_service() failed: NT_STATUS_INTERNAL_ERROR
smbXsrv_tcon_disconnect_all: count[1] errors[1] first[NT_STATUS_INTERNAL_ERROR]
smbXsrv_session_logoff(0xf9695c89): smb2srv_tcon_disconnect_all() failed: NT_STATUS_INTERNAL_ERROR
smbXsrv_session_logoff_all: count[1] errors[1] first[NT_STATUS_INTERNAL_ERROR]
Server exit (termination signal)
exit_server_common: smbXsrv_session_logoff_all() failed (NT_STATUS_INTERNAL_ERROR) - triggering cleanup
It's absolute nonsense; that directory exists at that exact location and the samba service doesn't actually exit. smbstatus shows it's running fine, just not connected.
Anyway, it's weird. I'll either figure it out or find a work around.