Webpack error on Heroku Deployment - ruby-on-rails

Question

Running my rails app locally works fine. Then I deployed it to Heroku successfully but when opening the app I get the error:
"We're sorry, but something went wrong.
If you are the application owner check the logs for more information."
I'm new to using Heroku, this is my first deployed app so not completely sure of how everything works. In my heroku logs it says that:
ActionView::Template::Error (Webpacker can't find application.css in
/app/public/packs/manifest.json. Possible causes:
You want to set webpacker.yml value of compile to true for your environment
Webpack has not yet re-run to reflect updates.
You have misconfigured Webpacker's config/webpacker.yml file. unless you are using the webpack -w or the webpack-dev-server.
Your Webpack configuration is not creating a manifest.
Anyone that has had the same problem or has any tips on how to try and solve this?
This is the whole heroku log:
2017-11-19T12:30:56.336758+00:00 app[web.1]: I, [2017-11-19T12:30:56.336675 #4] INFO -- : [0b584fb1-2c9e-41e9-bfe4-19cbf6523a6c] Started GET "/" for 85.228.31.12 at 2017-11-19 12:30:56 +0000
2017-11-19T12:30:56.338912+00:00 app[web.1]: I, [2017-11-19T12:30:56.338848 #4] INFO -- : [0b584fb1-2c9e-41e9-bfe4-19cbf6523a6c] Rendered react_view/index.html.erb within layouts/application (0.7ms)
2017-11-19T12:30:56.337434+00:00 app[web.1]: I, [2017-11-19T12:30:56.337362 #4] INFO -- : [0b584fb1-2c9e-41e9-bfe4-19cbf6523a6c] Processing by ReactViewController#index as HTML
2017-11-19T12:30:56.338062+00:00 app[web.1]: I, [2017-11-19T12:30:56.337995 #4] INFO -- : [0b584fb1-2c9e-41e9-bfe4-19cbf6523a6c] Rendering react_view/index.html.erb within layouts/application
2017-11-19T12:30:56.339074+00:00 app[web.1]: I, [2017-11-19T12:30:56.339014 #4] INFO -- : [0b584fb1-2c9e-41e9-bfe4-19cbf6523a6c] Completed 500 Internal Server Error in 2ms
2017-11-19T12:30:56.339692+00:00 app[web.1]: F, [2017-11-19T12:30:56.339632 #4] FATAL -- : [0b584fb1-2c9e-41e9-bfe4-19cbf6523a6c]
2017-11-19T12:30:56.339766+00:00 app[web.1]: F, [2017-11-19T12:30:56.339696 #4] FATAL -- : [0b584fb1-2c9e-41e9-bfe4-19cbf6523a6c] ActionView::Template::Error (Webpacker can't find application.css in /app/public/packs/manifest.json. Possible causes:
2017-11-19T12:30:56.339768+00:00 app[web.1]: 1. You want to set webpacker.yml value of compile to true for your environment
2017-11-19T12:30:56.339770+00:00 app[web.1]: 2. Webpack has not yet re-run to reflect updates.
2017-11-19T12:30:56.339771+00:00 app[web.1]: 3. You have misconfigured Webpacker's config/webpacker.yml file.
2017-11-19T12:30:56.339769+00:00 app[web.1]: unless you are using the `webpack -w` or the webpack-dev-server.
2017-11-19T12:30:56.339772+00:00 app[web.1]: 4. Your Webpack configuration is not creating a manifest.
2017-11-19T12:30:56.339974+00:00 app[web.1]: [0b584fb1-2c9e-41e9-bfe4-19cbf6523a6c] 3: <%= javascript_pack_tag 'application' %>
2017-11-19T12:30:56.340038+00:00 app[web.1]: F, [2017-11-19T12:30:56.339975 #4] FATAL -- : [0b584fb1-2c9e-41e9-bfe4-19cbf6523a6c]
2017-11-19T12:30:56.340104+00:00 app[web.1]: F, [2017-11-19T12:30:56.340050 #4] FATAL -- : [0b584fb1-2c9e-41e9-bfe4-19cbf6523a6c] app/views/react_view/index.html.erb:2:in `_app_views_react_view_index_html_erb___547572771215860275_34419720'
2017-11-19T12:30:56.339974+00:00 app[web.1]: [0b584fb1-2c9e-41e9-bfe4-19cbf6523a6c] 4: <%= javascript_pack_tag 'ReactHome' %>
2017-11-19T12:30:56.339773+00:00 app[web.1]: Your manifest contains:
2017-11-19T12:30:56.339775+00:00 app[web.1]: }
2017-11-19T12:30:56.339774+00:00 app[web.1]: {
2017-11-19T12:30:56.339775+00:00 app[web.1]: ):
2017-11-19T12:30:56.339972+00:00 app[web.1]: F, [2017-11-19T12:30:56.339903 #4] FATAL -- : [0b584fb1-2c9e-41e9-bfe4-19cbf6523a6c] 1: <script>window.__theme = 'bs4';</script>
2017-11-19T12:30:56.339973+00:00 app[web.1]: [0b584fb1-2c9e-41e9-bfe4-19cbf6523a6c] 2: <%= stylesheet_pack_tag 'application' %>
`

Answer 1

I had this error, tried to compile and also got :
$ rake assets:precompile RAILS_ENV=production
...
rails aborted!
No such middleware to insert after: ActionDispatch::Static
Solved it thanks to this thread by turning with an ENV
# config/environments/production.rb
config.public_file_server.enabled=true` # ENV['RAILS_SERVE_STATIC_FILES'].present?