When running "testparm -s" from CLI there is a message :
WARNING: The "syslog only" option is deprecated
Maybe this is an old option for SAMBA 3.X that is no longer available in SAMBA 4.X
From WEB GUI Services => SMB/CIFS => Advanced settings => Log level mine is set to Normal and I see no LOGs in /va/log/samba
I mean all log files have zero bytes.