Comment 4 for bug 1723956

Sure, here we go. It might be worth to note that this system was installed as 12.04 or 12.10 and dist-upgraded ever since, so maybe this would explain some oddities, although in general everything works just fine.

libc6:
  Installed: 2.24-9ubuntu2.2
  Candidate: 2.24-9ubuntu2.2
  Version table:
 *** 2.24-9ubuntu2.2 500
        500 http://ftp.fau.de/ubuntu zesty-updates/main amd64 Packages
        500 http://security.ubuntu.com/ubuntu zesty-security/main amd64 Packages
        100 /var/lib/dpkg/status
     2.24-9ubuntu2 500
        500 http://ftp.fau.de/ubuntu zesty/main amd64 Packages

With trial and error I could identify that libnss-resolve seems to be the problem. Removing it from the hosts line in nsswitch fixes the issue. Probably not the best fix but at least it can fall back to the resolver stub via the localhost resolv.conf entry for some caching. Unfortunately I can't upgrade to 17.10 yet until end of January to do additional testing.