samba - Mar 2018 - Specified domain does not exist or could not be contacted and IP6

Hi all.

I am setting ADDC on Debian 9 from default repo and have two questions. This is
my smb.conf

[global]
    netbios name = MYSERVER
    realm = MYSERVER.EXAMPLE.COM
    workgroup = MYDOMAIN
    dns forwarder = HERE_EXTERNAL_DNS
    server role = active directory domain controller
    idmap_ldb:use rfc2307 = yes

[netlogon]
    path = /var/lib/samba/sysvol/fileserver.ekostroyrus.ru/scripts
    read only = No

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

I can connect from my Windows 7 Active Directory users and computers and
everything works fine. Besides one thing. Almost on any action that I do in
Active Directory users and computers I firstly get specified domain does not
exist or could not be contacted. I press ok and continue work. I mean program
doesn't crash, and I do everything in it. This error is like info for every
action. You can do the action, but first you must read this info. How to fix it?

And the second question - how to disable IP6 in samba? Because I disabled IP6 in
Debian and get errors in samba logs.

Could anyone help me with these questions? I highly appreciate any help.

-- 
Best regards, Alex