Rails Tutorial13章でCarrierWaveを使って本番環境(heroku)での画像投稿の設定をした後デプロイできなくなりました。

Question

現在Cloud9上でRails Tutorialを勉強しているのですが、１３章で画像投稿のためのセッティングをして、git push heroku コマンドをしたところ、デプロイできませんでした。
現在の状況はCloud9上のサーバーでは画像投稿含めて正常に動作していて、テストも通っています。
AWSでIAMとS3バケットを作成して、herokuに環境変数を設定しました。

最初にデプロイした時にコンソール上のメッセージでfogではなくfog-awsというgemを使用するように指示があったため、以下の記事をもとに設定を行いました。
QiitaのCarrierWaveに関する記事
13章でデプロイできない旨の他の人の質問

デプロイした時のコンソール上のメッセージは以下の通りです。

ec2-user:~/rails-tutorial/sample_app09 (master) $ git push heroku
Counting objects: 17370, done.
Compressing objects: 100% (8539/8539), done.
Writing objects: 100% (17370/17370), 26.10 MiB | 24.34 MiB/s, done.
Total 17370 (delta 7601), reused 17314 (delta 7554)
remote: Compressing source files... done.
remote: Building source:
remote: 
remote:  !     Warning: Multiple default buildpacks reported the ability to handle this app. The first buildpack in the list below will be used.
remote:                         Detected buildpacks: Ruby,Node.js
remote:                         See https://devcenter.heroku.com/articles/buildpacks#buildpack-detect-order
remote: -----> Ruby app detected
remote: -----> Compiling Ruby/Rails
remote: -----> Using Ruby version: ruby-2.5.6
remote: -----> Installing dependencies using bundler 1.17.3
remote:        Running: bundle install --without development:test --path vendor/bundle --binstubs vendor/bundle/bin -j4 --deployment
remote:        The dependency tzinfo-data (>= 0) will be unused by any of the platforms Bundler is installing for. Bundler is installing for ruby but the dependency is only for x86-mingw32, x86-mswin32, x64-mingw32, java. To add those platforms to the bundle, run `bundle lock --add-platform x86-mingw32 x86-mswin32 x64-mingw32 java`.
remote:        Fetching gem metadata from https://rubygems.org/............
remote:        Fetching rake 13.0.0
remote:        Installing rake 13.0.0

省略

remote:        Fetching sass-rails 5.0.6
remote:        Installing sass-rails 5.0.6
remote:        Bundle complete! 29 Gemfile dependencies, 74 gems now installed.
remote:        Gems in the groups development and test were not installed.
remote:        Bundled gems are installed into `./vendor/bundle`
remote:        Post-install message from sass:
remote:        
remote:        Ruby Sass has reached end-of-life and should no longer be used.
remote:        
remote:        * If you use Sass as a command-line tool, we recommend using Dart Sass, the new
remote:          primary implementation: https://sass-lang.com/install
remote:        
remote:        * If you use Sass as a plug-in for a Ruby web framework, we recommend using the
remote:          sassc gem: https://github.com/sass/sassc-ruby#readme
remote:        
remote:        * For more details, please refer to the Sass blog:
remote:          https://sass-lang.com/blog/posts/7828841
remote:        
remote:        Bundle completed (50.05s)
remote:        Cleaning up the bundler cache.
remote: -----> Installing node-v10.15.3-linux-x64
remote: -----> Detecting rake tasks
remote: -----> Preparing app for Rails asset pipeline
remote:        Running: rake assets:precompile
remote:        rake aborted!
remote:        LoadError: cannot load such file -- fog
remote:        /tmp/build_680f40062a50379ed085c7412ffe8cba/vendor/bundle/ruby/2.5.0/gems/activesupport-5.1.6/lib/active_support/dependencies.rb:292:in `require'
remote:        /tmp/build_680f40062a50379ed085c7412ffe8cba/vendor/bundle/ruby/2.5.0/gems/activesupport-5.1.6/lib/active_support/dependencies.rb:292:in `block in require'
remote:        /tmp/build_680f40062a50379ed085c7412ffe8cba/vendor/bundle/ruby/2.5.0/gems/activesupport-5.1.6/lib/active_support/dependencies.rb:258:in `load_dependency'
remote:        /tmp/build_680f40062a50379ed085c7412ffe8cba/vendor/bundle/ruby/2.5.0/gems/activesupport-5.1.6/lib/active_support/dependencies.rb:292:in `require'
remote:        /tmp/build_680f40062a50379ed085c7412ffe8cba/vendor/bundle/ruby/2.5.0/gems/carrierwave-1.2.2/lib/carrierwave/uploader/configuration.rb:122:in `eager_load_fog'
remote:        /tmp/build_680f40062a50379ed085c7412ffe8cba/vendor/bundle/ruby/2.5.0/gems/carrierwave-1.2.2/lib/carrierwave/uploader/configuration.rb:137:in `fog_credentials='

省略

remote:        /tmp/build_680f40062a50379ed085c7412ffe8cba/vendor/bundle/ruby/2.5.0/gems/railties-5.1.6/lib/rails/application.rb:329:in `require_environment!'
remote:        /tmp/build_680f40062a50379ed085c7412ffe8cba/vendor/bundle/ruby/2.5.0/gems/railties-5.1.6/lib/rails/application.rb:445:in `block in run_tasks_blocks'
remote:        /tmp/build_680f40062a50379ed085c7412ffe8cba/vendor/bundle/ruby/2.5.0/gems/sprockets-rails-3.2.1/lib/sprockets/rails/task.rb:62:in `block (2 levels) in define'
remote:        /tmp/build_680f40062a50379ed085c7412ffe8cba/vendor/bundle/ruby/2.5.0/gems/rake-13.0.0/exe/rake:27:in `<top (required)>'
remote:        Tasks: TOP => environment
remote:        (See full trace by running task with --trace)
remote: 
remote:  !
remote:  !     Precompiling assets failed.
remote:  !
remote:  !     Push rejected, failed to compile Ruby app.
remote: 
remote:  !     Push failed
remote: Verifying deploy...
remote: 
remote: !       Push rejected to murmuring-dawn-26950.
remote: 
To https://git.heroku.com/murmuring-dawn-26950.git
 ! [remote rejected]   master -> master (pre-receive hook declined)
error: failed to push some refs to 'https://git.heroku.com/murmuring-dawn-26950.git'

Gemfileです。

source 'https://rubygems.org'

gem 'rails',                   '5.1.6'
gem 'bcrypt',                  '3.1.12'
gem 'faker',                   '1.7.3'
gem 'carrierwave',             '1.2.2'
gem 'mini_magick',             '4.7.0'
gem 'will_paginate',           '3.1.6'
gem 'bootstrap-will_paginate', '1.0.0'
gem 'bootstrap-sass',          '3.3.7'
gem 'puma',                    '3.9.1'
gem 'sass-rails',              '5.0.6'
gem 'uglifier',                '3.2.0'
gem 'coffee-rails',            '4.2.2'
gem 'jquery-rails',            '4.3.1'
gem 'turbolinks',              '5.0.1'
gem 'jbuilder',                '2.7.0'

group :development, :test do
  gem 'sqlite3', '1.3.13'
  gem 'byebug',  '9.0.6', platform: :mri
end

group :development do
  gem 'web-console',           '3.5.1'
  gem 'listen',                '3.1.5'
  gem 'spring',                '2.0.2'
  gem 'spring-watcher-listen', '2.0.1'
end

group :test do
  gem 'rails-controller-testing', '1.0.2'
  gem 'minitest',                 '5.10.3'
  gem 'minitest-reporters',       '1.1.14'
  gem 'guard',                    '2.14.1'
  gem 'guard-minitest',           '2.4.6'
end

group :production do
  gem 'pg',   '0.20.0'
  gem 'fog-aws'
end

# Windows環境ではtzinfo-dataというgemを含める必要があります
gem 'tzinfo-data', platforms: [:mingw, :mswin, :x64_mingw, :jruby]

sample_app/config/initializers/carrier_wave.rbの設定です。

if Rails.env.production?
  require 'carrierwave/storage/abstract'
  require 'carrierwave/storage/file'
  require 'carrierwave/storage/fog'
  CarrierWave.configure do |config|
    config.fog_credentials = {
      # Amazon S3用の設定
      :provider              => 'AWS',
      :region                => ENV['ap-northeast-1'],     # 例: 'ap-northeast-1'
      :aws_access_key_id     => ENV['割愛'],
      :aws_secret_access_key => ENV['割愛']
    }
    config.fog_directory     =  ENV['割愛']
    config.storage :fog
    config.fog_provider = 'fog/aws'
  end
end

sample_app/app/uploaders/picture_uploader.rbの設定です。

class PictureUploader < CarrierWave::Uploader::Base
  include CarrierWave::MiniMagick
  process resize_to_limit: [400, 400]
  
  # Choose what kind of storage to use for this uploader:
  if Rails.env.production?
    storage :fog
  else
    storage :file
  end
  # storage :fog

  # Override the directory where uploaded files will be stored.
  # This is a sensible default for uploaders that are meant to be mounted:
  def store_dir
    "uploads/#{model.class.to_s.underscore}/#{mounted_as}/#{model.id}"
  end

  # Add a white list of extensions which are allowed to be uploaded.
  # For images you might use something like this:
  def extension_whitelist
    %w(jpg jpeg gif png)
  end
end

１２章が終わった時点でローカル環境の調子が悪くなり、１３章からCloud9に引越ししました。あと、最初にデプロイできなかった時に、もともと作成していたherokuのリモートディレクトリと齟齬があったことが原因かと思って、紐づけを解除してheroku createで新たにheroku上にディレクトリを作りました。その事が関係あるのか分かりませんが一応情報としてお伝えします。
何を調べてよいのか見当がつかないので、何かアドバイスが頂ければありがたいです。
よろしくお願いいたします。