Nginx – trying to diagnose weird nginx 110 connection timeout error somehow related to redirection

I'm trying to diagnose server timeouts on ubuntu 16.04. I've seen this site http://blogs.candoerz.com/question/161218/cannot-figure-out-nginx–puma-timeout-110-connection-timed-out.aspx
and suggestions given there didn't work. However the site does not address the problem I'm concerned with:

one part of the error log looks particularly strange

upstream: "http://unix:///home/chris/Rails/chrisbim2ree/shared/tmp/sockets/chrisbim2ree-puma.sock/contact_messages"

As far as I understand sockets are files, not directories. Here the log seems to indicate that it is a directory. The other website I mention here has similar pattern. On my system *puma.sock is not a directory. What's wrong here? Problem happens on a part of the site responsible for redirection after submitting the message.

tmp/sockets$ ls -l
total 0
srwxrwxrwx 1 chris chris 0 Jun 21 20:08 chrisbim2ree-puma.sock

my error log.
$ tail -n 2 ./log/nginx.error.log

2016/06/21 20:10:30 [error] 1416#1416: *5 upstream timed out (110: Connection timed out) while reading response header from upstream,

client: 86.22.165.132, server: chrisbeard-images.com, request: "POST
/contact_messages HTTP/1.1", upstream:
"http://unix:///home/chris/Rails/chrisbim2ree/shared/tmp/sockets/chrisbim2ree-puma.sock/contact_messages",
host: "chrisbeard-images.com", referrer:
"http://chrisbeard-images.com/contact"
2016/06/21 20:13:41 [info] 1416#1416: *14 client closed connection while waiting for request, client: 86.22.165.132, server: 0.0.0.0:80

nginx config files

$ sudo cat /etc/nginx/sites-enabled/default 
[sudo] password for chris: 

upstream puma {
  server unix:///home/chris/Rails/chrisbim2ree/shared/tmp/sockets/chrisbim2ree-puma.sock;
}

server {
  listen 80 default_server deferred;
  server_name chrisbeard-images.com www.chrisbeard-images.com;

  root /home/chris/Rails/chrisbim2ree/current/public;
  access_log /home/chris/Rails/chrisbim2ree/current/log/nginx.access.log;
  error_log /home/chris/Rails/chrisbim2ree/current/log/nginx.error.log info;

  location ^~ /assets/ {
    gzip_static on;
    expires max;
    add_header Cache-Control public;
  }

  try_files $uri/index.html $uri @puma;

  location @puma {
    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    proxy_set_header Host $http_host;
    proxy_redirect off;

    proxy_pass http://puma;
  }

  error_page 500 502 503 504 /500.html;
  client_max_body_size 4G;
  keepalive_timeout 70s;
}

another relevant config file

$ sudo cat /etc/nginx/nginx.conf
user www-data;
worker_processes 1;
pid /var/run/nginx.pid;

events { worker_connections 1024; }

http {
        client_max_body_size 2048M;
    sendfile on;
    tcp_nopush on;
    tcp_nodelay on;
    keepalive_timeout 70;
    types_hash_max_size 2048;
    server_tokens off;

    # server_names_hash_bucket_size 64;
    # server_name_in_redirect off;

    include /etc/nginx/mime.types;
    default_type application/octet-stream;

    access_log /var/log/nginx/access.log;
    error_log /var/log/nginx/error.log;

    gzip on;
    gzip_disable "msie6";
    gzip_types text/plain text/xml text/css text/comma-separated-values;
        upstream app_server { server 127.0.0.1:8080 fail_timeout=0; }

    include /etc/nginx/conf.d/*.conf;
    include /etc/nginx/sites-enabled/*;
}

puma config

$ cat ./puma.rb
#!/usr/bin/env puma

directory '/home/chris/Rails/chrisbim2ree/current'
rackup "/home/chris/Rails/chrisbim2ree/current/config.ru"
environment 'production'

pidfile "/home/chris/Rails/chrisbim2ree/shared/tmp/pids/puma.pid"
state_path "/home/chris/Rails/chrisbim2ree/shared/tmp/pids/puma.state"
stdout_redirect '/home/chris/Rails/chrisbim2ree/current/log/puma.error.log', '/home/chris/Rails/chrisbim2ree/current/log/puma.access.log', true


threads 4,16

bind 'unix:///home/chris/Rails/chrisbim2ree/shared/tmp/sockets/chrisbim2ree-puma.sock'

workers 4



preload_app!


on_restart do
  puts 'Refreshing Gemfile'
  ENV["BUNDLE_GEMFILE"] = "/home/chris/Rails/chrisbim2ree/current/Gemfile"
end


on_worker_boot do
  ActiveSupport.on_load(:active_record) do
    ActiveRecord::Base.establish_connection
  end
end