If you look at the gitlab error log in
/var/log/gitlab/nginx, you¹ll find lots of messages like these:
2015/06/16 11:27:24 [crit] 28935#0: *140 connect() to
unix:/var/opt/gitlab/gitlab-rails/sockets/gitlab.socket failed (2: No such file
or directory) while connecting to upstream,
Looks like something internal to gitlab is hosed.