OK, screening of logfile for TV IP results in two errors within /var/log/samba/log.172.17.0.53
[2018/09/04 21:14:31.545299, 0] ../source3/auth/auth_domain.c:122(connect_to_domain_password_server) connect_to_domain_password_server: unable to open the domain client session to machine NSDC-EBB-S01.AD.EBBINGHAUS.WORLD. Error was : NT_STATUS_NETWORK_ACCESS_DENIED. [2018/09/04 21:14:31.611424, 0] ../source3/auth/auth_domain.c:226(domain_client_validate) domain_client_validate: unable to validate password for user GUEST in domain WORKGROUP to Domain controller NSDC-EBB-S01.AD.EBBINGHAUS.WORLD. Error was NT_STATUS_NO_SUCH_USER.
Second error is related to a guest user as this is the default setting on the Panasonic TV. This does occur in 99 of 100 caes.
The first error is something I can not assign. There was just one error of this type.
I also found errors in message.log:
Sep 4 22:09:15 ebb-s01 smbd[18920]: domain_client_validate: unable to validate password for user SONOS in domain NODOMAIN to Domain controller NSDC-EBB-S01.AD.MYNAME.TLD. Error was NT_STATUS_NO_SUCH_USER.