Ruby on Rails - 504 Gateway Time-out nginx/1.1.19

I have a website that was working this morning and now wont load, this is the error I get when I try to browse.

Operating system is Ubuntu LTS 12.04 and it's Ruby on Rails.

From what I know Nginx is running as a proxy for apache, unicorn is passing the ruby on rails site to it

There is an error log for unicorn (unicorn.log) which identifies the error

", [2021-03-23T17:18:40.425643 #3852] ERROR -- : reaped # worker=5
I, [2021-03-23T17:18:40.425794 #3852] INFO -- : worker=5 spawning...
I, [2021-03-23T17:18:40.451441 #15265] INFO -- : worker=5 spawned pid=15265
I, [2021-03-23T17:18:40.451720 #15265] INFO -- : Refreshing Gem list
E, [2021-03-23T17:18:41.348767 #15185] ERROR -- : uninitialized constant ApplicationController (NameError)
/home/deployer/apps/kcp/releases/10/vendor/plugins/edge/app/controllers/admin/base_controller.http://rb:3:in `'
/home/deployer/apps/kcp/releases/10/vendor/plugins/edge/app/controllers/admin/about_controller.http://rb:1:in `'
/home/deployer/apps/kcp/releases/10/vendor/bundle/ruby/1.9.1/gems/railties-3.1.12/lib/rails/engine.http://rb:417:in `block (2 levels) in eager_load!'
/home/deployer/apps/kcp/releases/10/vendor/bundle/"


Can someone assist please?