Rails App On Heroku - Status 500 Error => Blank White Page - ruby-on-rails

Question

I have a Rails app on Heroku staging server and everything has gone well except for the error pages aren't working. Every time I get a "status: 500" error, it results in a blank white page, NOT the 500.html static error page.
I have a static 500.html page in the my_app/public folder, and I can access it in heroku if I try to do so directly via myapp.herokuapp.com/500. It will display fine then. But if I get a real "status: 500" error in the program, it will not render the 500.html page... rather, it renders a blank white page.
To create an error, I attempted to go to a non-existent page.
The logs indicate that the "status: 500" error has occured, but again, white page. Here is part of the output from the logs:
heroku[router]: at=info method=GET path="/fakepage" host=myapp.herokuapp.com request_id=20825-b474-4e-37f-c52486140 fwd="67.xxx.xxx.x" dyno=web.1 connect=1ms service=108ms status=500 bytes=949
Started GET "/fakepage" for xx.xxx.xxx.x at 2014-08-24 03:50:31 +0000
app[web.1]: ** [Raven] User excluded error: #<ActionController::RoutingError: No route matches [GET] "/fakepage">
In the config/environment/staging.rb I have the following:
config.consider_all_requests_local = false
config.serve_static_assets = true #after the default of false didn't work
It seems like this shouldn't be one of those "tough issues"... and not finding any prior posts or articles that directly related to my question makes me think it must be something inane on my part. I'm currently running Ruby 2.0.0p451 & Rails 4.1.1. I have Sentry setup through heroku for monitoring errors. Let me know if there's any other useful info I could provide.
EDIT
I should mention that my Gemfile looks like this:
source 'https://rubygems.org'
ruby '2.0.0'
gem 'rails' #, '4.1.1'
gem 'bcrypt'
gem 'bootstrap_form'
gem 'bootstrap-sass'
gem 'carrierwave'
gem 'coffee-rails'
gem 'dropzonejs-rails'
gem 'email_validator'
gem 'fog'
gem 'geocoder'
gem 'haml-rails'
gem 'jquery-rails'
gem 'jquery-turbolinks'
gem 'jquery-ui-rails'
gem 'mini_magick'
gem 'paratrooper'
gem 'sass-rails'
gem 'sidekiq'
gem 'sinatra', require: nil
gem 'turbolinks'
gem 'uglifier'
gem 'unicorn'
group :production, :staging do
gem 'pg'
gem 'rails_12factor'
gem 'sentry-raven'
end
That is, I do have the gem 'rails_12factor' in the correct group for both staging & production environments as noted in a similar question regarding serving static assets in heroku with Rails4... essentially what an error page would be doing.
I have the app setup to run multiple processes through Unicorn, and have Unicorn temporarily setup to handle Sidekiq processes internally while the app is in testing (to avoid a second dyno). Also running Redis.
config/environments/staging.rb
Rails.application.configure do
config.cache_classes = true
config.eager_load = true
config.consider_all_requests_local = false
config.action_controller.perform_caching = true
config.serve_static_assets = true
config.assets.js_compressor = :uglifier
config.assets.compress = true
config.assets.compile = true #WAS FALSE
config.assets.digest = true
config.assets.version = '1.0'
config.action_mailer.default_url_options = { host: "..." }
config.action_mailer.delivery_method = :smtp
ActionMailer::Base.smtp_settings = {
:port => ENV['MAILGUN_SMTP_PORT' ],
:address => ENV['MAILGUN_SMTP_SERVER' ],
:user_name => ENV['MAILGUN_SMTP_LOGIN' ],
:password => ENV['MAILGUN_SMTP_PASSWORD'],
:domain => '...',
:authentication => :plain }
config.log_level = :info #see everything in the log
config.i18n.fallbacks = true
config.log_formatter = ::Logger::Formatter.new
config.action_dispatch.show_exceptions = false #per sentry-raven docs
config.active_record.dump_schema_after_migration = false
config.active_support.deprecation = :notify #send to registered listeners

Answer 1

I finally got to the bottom of the issue.
The conclusion is that Heroku will serve the basic error pages when a status error (404, 500, etc) happens in a vanilla Rails application without any custom classes. After I determined that, it helped direct the diagnosis.
Looking through the config/environments/staging.rb code, I saw the LOC that sentry-raven stipulated in their docs should be set to false:
config.action_dispatch.show_exceptions = false #per sentry-raven docs
After setting this back to true, the status error pages started functioning:
config.action_dispatch.show_exceptions = true #status error pages work again!
So, I may have been misunderstanding sentry-raven's docs & incorporating it incorrectly into the Rails app configs, or something otherwise, but that's what the issue turned out to be.
So, if you your Heroku hosted Rails app is performing fine and then runs into the "white screen of death" upon any status error, this is one more thing to check in your attempts to diagnose.