This issue does not have enough information to determine what is wrong. It is however fairly clear that it is not related to "scutil --get HostName" mentioning that there is no hostname set as that is the normal state of systems, and I have never run into the problem mentioned here (and have used macOS exclusively from one of the earliest public beta's of macOS 10.0).

My gut feeling is that this is some issue with your system or environment.

Some more questions:

- Is this is a consistent problem, or only on some networks?
- Do you have any custom settings in the Networking preference pane related to name resolution (extra search domains, DNS servers, ...)?
- Do the domains returned by the DHCP server actually exist?
- Likewise for the DNS servers
- Does the result of socket.gethostname() look sane? In particular, does this include a domain name?
- The original message mentions: "and that the DHCP servers provides one ore more domains to be useles for resolution.". What is meant by that? AFAIK the DHCP server can only return 1 domain name, not a full DNS search list (or at least not one that is used by most major platforms).