[Samba] samba AD not working

[Sonic]

More info:

Attempting to connect via smbclient using hostnames fail:
=================
$ smbclient -L localhost -U%
protocol negotiation failed: NT_STATUS_INVALID_NETWORK_RESPONSE
=================
... doesn't matter whether I use localhost, or ad, or
ad.office.mydomain.com (local, short or full).

However, via IP address:
=================
/usr/local/samba/var# smbclient -L 172.26.62.31 -U%
Domain=[MYDOMAIN] OS=[] Server=[]

        Sharename       Type      Comment
        ---------       ----      -------
        netlogon        Disk
        sysvol          Disk
        IPC$            IPC       IPC Service (Samba 4.6.5)
Domain=[MYDOMAIN] OS=[] Server=[]

        Server               Comment
        ---------            -------

        Workgroup            Master
        ---------            -------
=================
... and I can successfully use 127.0.0.1 as well.

All DNS tests pass, SRV records, etc. are all there. So this is quite confusing.