samba - May 2020 - errors during samba_dnsupdate, another case

Hi,

I installed my first Samba 4.12 AD with packages from 
https://www.sernet.de/ on CentOS 8. Everything seems to work OK, 
including DNS records being created for members that join the domain.

Reading https://wiki.samba.org I came across 
https://wiki.samba.org/index.php/Testing_Dynamic_DNS_Updates. When I 
execute "samba_dnsupdate --verbose --all-names" on the DC I'm
seeing the
same errors Daniel Betschart reported on this list on 2020-04-06:

[root at dc01 ~]# samba_dnsupdate --all-names --fail-immediately
; TSIG error with server: tsig verify failure
[root at dc01 ~]# samba_dnsupdate --all-names --fail-immediately 
--use-samba-tool
ERROR(runtime): uncaught exception - (9711, 
'WERR_DNS_ERROR_RECORD_ALREADY_EXISTS')
   File "/usr/lib64/python3.6/site-packages/samba/netcmd/__init__.py",
line 186, in _run
     return self.run(*args, **kwargs)
   File "/usr/lib64/python3.6/site-packages/samba/netcmd/dns.py", line
945, in run
     raise e
   File "/usr/lib64/python3.6/site-packages/samba/netcmd/dns.py", line
941, in run
     0, server, zone, name, add_rec_buf, None)

Rowland Penny explained that this could be ignored because Daniel 
Betschart joined a Windows DC, but I'm getting these errors on a Linux 
DC. I don't seem to have a real DNS update problem, because I have

[2020/05/12 14:46:38.288004,  3] 
../../source4/dsdb/dns/dns_update.c:111(dnsupdate_spnupdate_done)
   samba_runcmd_io_handler: Child /usr/sbin/samba_dnsupdate exited 0
[2020/05/12 14:46:38.410990,  3] 
../../source4/dsdb/dns/dns_update.c:88(dnsupdate_nameupdate_done)
   Completed DNS update check OK

in /var/log/samba/log.samba for the automatic updates. Still I would 
like to have the error above explained. Please tell me which 
configuration details you need.

Thanks a lot
Matthias