[Samba] auth_json_audit is not logging to a custom log file

[shacky]

Hi,
I'm using Samba 4.7.6 on Ubuntu 18.04 LTS (unfortunately I cannot upgrade
at the moment because I'm using Zentyal which is locked here) and I'm
trying to enable JSON Auth logging.

If I add this in my Samba configuration I cannot get auth JSON logged to
the main Samba log file (/var/log/samba/samba.log):
==================================================
log file = /var/log/samba/samba.log
log level = 3 auth_json_audit:3
max log size = 100000
==================================================

But if I try to specify a dedicated log file for JSON auth logs they are
not  logged to the specified log file:
==================================================
log file = /var/log/samba/samba.log
log level = 3 auth_audit:3 auth_json_audit:3@/var/log/samba/auth_audit.log
max log size = 100000
==================================================

Could you help me to understand where I'm wrong, please?

Thank you very much!

Bye