Gitlab 8 with nginx proxy can't download a zip, clone a public repo as guest, can't build in CI either

It looks as though downloading of ZIP-Files is now handled by the gitlab-workhorse.

For that there's some extra stuff in the nginx-configfile. You might want to have a look at https://gitlab.com/gitlab-org/gitlab-ce/blob/master/lib/support/nginx/gitlab where there is a section

upstream gitlab-workhorse {
  server unix:/home/git/gitlab/tmp/sockets/gitlab-workhorse.socket fail_timeout=0;
}

and a

proxy_pass http://gitlab-workhorse;

at the end of the configuration.

I'm currently digging into the same issue and will report back, when I've solved it.