[Samba] wbinfo not resolving SID to username

[Ing. Claudio Nicora]

I suspect there's something wrong in wbinfo on a freshly installed Samba 
AD Domain Controller on Ubuntu 18.04 server.
wbinfo does not resolve Windows SID to usernames:

# wbinfo -S S-1-5-21-299502267-616249376-1417001333-14107
3000103

I should see "SAMDOM\username" instead of "3000103", right?

getfacls has the same behavior:

# getfacl /var/lib/samba/sysvol
# file: var/lib/samba/sysvol
# owner: root
# group: 3000073
user::rwx
user:root:rwx
user:3000000:rwx
user:3000013:r-x
user:3000014:r-x
user:3000073:rwx
group::rwx
group:3000000:rwx
group:3000013:r-x
group:3000014:r-x
group:3000073:rwx
mask::rwx
other::---
default:user::rwx
default:user:root:rwx
default:user:3000000:rwx
default:user:3000013:r-x
default:user:3000014:r-x
default:user:3000073:rwx
default:group::---
default:group:3000000:rwx
default:group:3000013:r-x
default:group:3000014:r-x
default:group:3000073:rwx
default:mask::rwx
default:other::---

What's wrong?

Some other info below:

# lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 18.04 LTS
Release:        18.04
Codename:       bionic

# samba --version
Version 4.7.6-Ubuntu

# cat /etc/samba/smb.conf
[global]
         bind interfaces only = Yes
         interfaces = lo eth_lan
         netbios name = SRVADDC
         realm = SAMDOM.LOCAL
         server role = active directory domain controller
         server services = s3fs, rpc, nbt, wrepl, ldap, cldap, kdc, 
drepl, winbindd, ntp_signd, kcc, dnsupdate
         workgroup = SAMDOM
         winbind enum users = yes
         winbind enum groups = yes
         winbind use default domain = Yes

         # logging
         log level = 4
         log file = /var/log/samba/samba.log.%m
         debug timestamp = yes

         # Cap the size of the individual log files (in KiB).
         max log size = 10000

[netlogon]
         path = /var/lib/samba/sysvol/samdom.local/scripts
         read only = No

[sysvol]
         path = /var/lib/samba/sysvol
         read only = No