[Samba] [NTLMv2] status [NT_STATUS_NO_SUCH_USER]

[lists at zxt10d.de]

Good morning list,

as our first domain member runs fine for quite some weeks I set-up a 
second one yesterday, exactly as I set-up the first one (at least I 
think so ;)) using 
https://wiki.samba.org/index.php/Setting_up_Samba_as_a_Domain_Member

But I can't connect to it, in /var/log/samba/samba_auth_audit.log can be 
found:
[2022/06/22 09:12:56.496441,  2] 
../../auth/auth_log.c:647(log_authentication_event_human_readable)
   Auth: [SMB2,(null)] user [.]\[USERNAME] at [Mi, 22 Jun 2022 
09:12:56.496403 CEST] with [NTLMv2] status [NT_STATUS_NO_SUCH_USER] 
workstation [DESKTOP-76IGOT6] remote host ...

Testing the connection to the ADDC using:

wbinfo --ping-dc
checking the NETLOGON for domain[DOMAIN] dc connection to 
"dc1.DOMAIN.de" succeeded

getent hosts HOSTNAME
10.147.166.6    HOSTNAME.afp.DOMAIN.de HOSTNAME

getent hosts 1st member server
10.147.166.6    1STMS.afp.DOMAIN.de 1STMS

getent group DOMAIN\\AFP_ALL
DOMAIN\afp_all:x:115702:

getent passwd DOMAIN\\USERNAME
DOMAIN\USERNAME:*:230224:310513::/srv/samba/users/USERNAME:/bin/bash

/etc/krb5.conf looks fine for me.
/etc/samba/smb.conf is the same as on first member server
/etc/nsswitch.conf is modified as written in 
https://wiki.samba.org/index.php/Setting_up_Samba_as_a_Domain_Member

Adding the system to AD worked ...:
samba-tool domain join DOMAIN MEMBER -U"DOMAIN\sec_account"
Password for [DOMAIN\sec_account]:
libnet_join_precreate_machine_acct: Machine account successfully created
      join: struct secrets_domain_infoB
         [...]
ldb: Unable to open tdb '/var/lib/samba/private/secrets.ldb': No such 
file or directory
ldb: Failed to connect to '/var/lib/samba/private/secrets.ldb' with 
backend 'tdb': Unable to open tdb '/var/lib/samba/private/secrets.ldb': 
No such file or directory
Joined domain DOMAIN (S-1-5-21-854245398-484763869-1343024091)

smbd -V
Version 4.15.7-Debian

What did I wrong?

Have a nice day! :)
Torsten