Gitlab 8.2.1 - 504 timeout viewing merge request (110: Connection timed out)

Gitlab version: 8.2.1
Nginx version: 1.4.6

We recently upgraded from Gitlab 7.14.0 to Gitlab 8.2.1 on a 16GB/8cpu VM at DigitalOcean. We have one Merge Request with 55 comments that simply won’t load in the browser. All other merge_requests load fine. This is repeatable, and we’ve been unable to view this merge request at all in the browser. We get the following error from NGINX:

2015/12/02 14:49:02 [error] 9094#0: *62 upstream timed out (110: Connection timed out) while reading response header from upstream, client: x.x.x.x, server:, request: "GET /group/project/merge_requests/854 HTTP/1.1", upstream: "http://unix:/home/git/gitlab/tmp/sockets/gitlab.socket/group/project/merge_requests/900", host: ""

(Our errors are different from this question: Page timeouts when accessing merge request (502))

In config/unicorn.rb we have set timeout 1200 (up from an original 30, then tried 300 and 600). 600 was working well with Gitlab 7.14.0. We have worker_processes 12 also set in config/unicorn.rb.

Gitlab 8.2.1 uses gitlab-workhorse, but I’m not familiar enough with gitlab-workhorse to know if there are settings for it.

Our workhorse settings in Nginx:

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

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

location @gitlab-workhorse {
    client_max_body_size 0;
    gzip off;

    proxy_read_timeout      600;
    proxy_connect_timeout   600;
    proxy_redirect          off;
    proxy_buffering off;
    proxy_set_header    Host                $http_host;
    proxy_set_header    X-Real-IP           $remote_addr;
    proxy_set_header    X-Forwarded-Ssl     on;
    proxy_set_header    X-Forwarded-For     $proxy_add_x_forwarded_for;
    proxy_set_header    X-Forwarded-Proto   $scheme;
    proxy_pass http://gitlab-workhorse;

Output from free:

         total       used       free     shared    buffers     cached
Mem:      16433928   11946992    4486936     119052     236972    8130620
-/+ buffers/cache:    3579400   12854528

We’ve restarted Gitlab with service gitlab restart in the hopes there was a hungry resource, but we saw no difference.

Any suggestions on how we figure out what is going on and fix this issue?