便利だと思い rails_admin をインストールしましたが、それ以降Herokuにpushしようとすると、
タイトルのエラーが出るようになってしまいました。

localhost:3000 でのRailsAdminの画面は正常に表示されております。
(localhost:3000/rails_admin でアクセスできるように設定しています)

インストール時の手順は以下の通りで、エラーは出ませんでした。

  • Gemfileにgem 'rails_admin'を追加
  • bundle install を実行
  • rails g rails_admin:install を実行

また、単体で rake assets:precompile を実行した場合もエラーは出ません。

一度rails_admin自体を削除してみようと思い、以下を実行しましたが、エラー内容は全く変わりませんでした。

  • Gemfileから消去後に bundle install
  • config/initializers/rails_admin.rbファイルを消去
  • routes.rbからrails_adminについて書かれた行を消去
  • ターミナル再起動

プロジェクト内を検索してもRailsAdminは存在してないのに、このようなエラーが出ることも不思議です。どこに残っているんでしょうか。

config/environments/production.rb

Rails.application.configure do
...
  config.assets.initialize_on_precompile = false
...
end

エラーメッセージ

   ・・・・・・
    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:        NameError: uninitialized constant RailsAdmin
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/vendor/bundle/ruby/2.5.0/gems/bootsnap-1.4.5/lib/bootsnap/load_path_cache/core_ext/active_support.rb:79:in `block in load_missing_constant'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/vendor/bundle/ruby/2.5.0/gems/bootsnap-1.4.5/lib/bootsnap/load_path_cache/core_ext/active_support.rb:8:in `without_bootsnap_cache'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/vendor/bundle/ruby/2.5.0/gems/bootsnap-1.4.5/lib/bootsnap/load_path_cache/core_ext/active_support.rb:79:in `rescue in load_missing_constant'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/vendor/bundle/ruby/2.5.0/gems/bootsnap-1.4.5/lib/bootsnap/load_path_cache/core_ext/active_support.rb:58:in `load_missing_constant'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/config/initializers/rails_admin.rb:1:in `<top (required)>'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/vendor/bundle/ruby/2.5.0/gems/bootsnap-1.4.5/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:54:in `load'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/vendor/bundle/ruby/2.5.0/gems/bootsnap-1.4.5/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:54:in `load'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/vendor/bundle/ruby/2.5.0/gems/railties-5.2.3/lib/rails/engine.rb:657:in `block in load_config_initializer'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/vendor/bundle/ruby/2.5.0/gems/activesupport-5.2.3/lib/active_support/notifications.rb:170:in `instrument'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/vendor/bundle/ruby/2.5.0/gems/railties-5.2.3/lib/rails/engine.rb:656:in `load_config_initializer'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/vendor/bundle/ruby/2.5.0/gems/railties-5.2.3/lib/rails/engine.rb:614:in `block (2 levels) in <class:Engine>'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/vendor/bundle/ruby/2.5.0/gems/railties-5.2.3/lib/rails/engine.rb:613:in `each'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/vendor/bundle/ruby/2.5.0/gems/railties-5.2.3/lib/rails/engine.rb:613:in `block in <class:Engine>'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/vendor/bundle/ruby/2.5.0/gems/railties-5.2.3/lib/rails/initializable.rb:32:in `instance_exec'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/vendor/bundle/ruby/2.5.0/gems/railties-5.2.3/lib/rails/initializable.rb:32:in `run'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/vendor/bundle/ruby/2.5.0/gems/railties-5.2.3/lib/rails/initializable.rb:61:in `block in run_initializers'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/vendor/bundle/ruby/2.5.0/gems/railties-5.2.3/lib/rails/initializable.rb:50:in `each'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/vendor/bundle/ruby/2.5.0/gems/railties-5.2.3/lib/rails/initializable.rb:50:in `tsort_each_child'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/vendor/bundle/ruby/2.5.0/gems/railties-5.2.3/lib/rails/initializable.rb:60:in `run_initializers'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/vendor/bundle/ruby/2.5.0/gems/railties-5.2.3/lib/rails/application.rb:361:in `initialize!'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/config/environment.rb:5:in `<top (required)>'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/vendor/bundle/ruby/2.5.0/gems/bootsnap-1.4.5/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:22:in `require'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/vendor/bundle/ruby/2.5.0/gems/bootsnap-1.4.5/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:22:in `block in require_with_bootsnap_lfi'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/vendor/bundle/ruby/2.5.0/gems/bootsnap-1.4.5/lib/bootsnap/load_path_cache/loaded_features_index.rb:92:in `register'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/vendor/bundle/ruby/2.5.0/gems/bootsnap-1.4.5/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:21:in `require_with_bootsnap_lfi'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/vendor/bundle/ruby/2.5.0/gems/bootsnap-1.4.5/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:30:in `require'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/vendor/bundle/ruby/2.5.0/gems/railties-5.2.3/lib/rails/application.rb:337:in `require_environment!'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/vendor/bundle/ruby/2.5.0/gems/railties-5.2.3/lib/rails/application.rb:520:in `block in run_tasks_blocks'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/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_c2ae8846056c84a4ee0f6bc61a2fc8b4/vendor/bundle/ruby/2.5.0/gems/rake-12.3.3/exe/rake:27:in `<top (required)>'
        remote:        
        remote:        Caused by:
        remote:        NameError: uninitialized constant RailsAdmin
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/vendor/bundle/ruby/2.5.0/gems/bootsnap-1.4.5/lib/bootsnap/load_path_cache/core_ext/active_support.rb:60:in `block in load_missing_constant'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/vendor/bundle/ruby/2.5.0/gems/bootsnap-1.4.5/lib/bootsnap/load_path_cache/core_ext/active_support.rb:16:in `allow_bootsnap_retry'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/vendor/bundle/ruby/2.5.0/gems/bootsnap-1.4.5/lib/bootsnap/load_path_cache/core_ext/active_support.rb:59:in `load_missing_constant'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/config/initializers/rails_admin.rb:1:in `<top (required)>'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/vendor/bundle/ruby/2.5.0/gems/bootsnap-1.4.5/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:54:in `load'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/vendor/bundle/ruby/2.5.0/gems/bootsnap-1.4.5/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:54:in `load'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/vendor/bundle/ruby/2.5.0/gems/railties-5.2.3/lib/rails/engine.rb:657:in `block in load_config_initializer'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/vendor/bundle/ruby/2.5.0/gems/activesupport-5.2.3/lib/active_support/notifications.rb:170:in `instrument'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/vendor/bundle/ruby/2.5.0/gems/railties-5.2.3/lib/rails/engine.rb:656:in `load_config_initializer'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/vendor/bundle/ruby/2.5.0/gems/railties-5.2.3/lib/rails/engine.rb:614:in `block (2 levels) in <class:Engine>'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/vendor/bundle/ruby/2.5.0/gems/railties-5.2.3/lib/rails/engine.rb:613:in `each'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/vendor/bundle/ruby/2.5.0/gems/railties-5.2.3/lib/rails/engine.rb:613:in `block in <class:Engine>'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/vendor/bundle/ruby/2.5.0/gems/railties-5.2.3/lib/rails/initializable.rb:32:in `instance_exec'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/vendor/bundle/ruby/2.5.0/gems/railties-5.2.3/lib/rails/initializable.rb:32:in `run'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/vendor/bundle/ruby/2.5.0/gems/railties-5.2.3/lib/rails/initializable.rb:61:in `block in run_initializers'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/vendor/bundle/ruby/2.5.0/gems/railties-5.2.3/lib/rails/initializable.rb:50:in `each'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/vendor/bundle/ruby/2.5.0/gems/railties-5.2.3/lib/rails/initializable.rb:50:in `tsort_each_child'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/vendor/bundle/ruby/2.5.0/gems/railties-5.2.3/lib/rails/initializable.rb:60:in `run_initializers'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/vendor/bundle/ruby/2.5.0/gems/railties-5.2.3/lib/rails/application.rb:361:in `initialize!'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/config/environment.rb:5:in `<top (required)>'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/vendor/bundle/ruby/2.5.0/gems/bootsnap-1.4.5/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:22:in `require'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/vendor/bundle/ruby/2.5.0/gems/bootsnap-1.4.5/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:22:in `block in require_with_bootsnap_lfi'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/vendor/bundle/ruby/2.5.0/gems/bootsnap-1.4.5/lib/bootsnap/load_path_cache/loaded_features_index.rb:92:in `register'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/vendor/bundle/ruby/2.5.0/gems/bootsnap-1.4.5/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:21:in `require_with_bootsnap_lfi'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/vendor/bundle/ruby/2.5.0/gems/bootsnap-1.4.5/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:30:in `require'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/vendor/bundle/ruby/2.5.0/gems/railties-5.2.3/lib/rails/application.rb:337:in `require_environment!'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/vendor/bundle/ruby/2.5.0/gems/railties-5.2.3/lib/rails/application.rb:520:in `block in run_tasks_blocks'
        remote:        /tmp/build_c2ae8846056c84a4ee0f6bc61a2fc8b4/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_c2ae8846056c84a4ee0f6bc61a2fc8b4/vendor/bundle/ruby/2.5.0/gems/rake-12.3.3/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 komo-service.
        remote: 
        To https://git.heroku.com/komo-service.git
         ! [remote rejected] master -> master (pre-receive hook declined)
        error: failed to push some refs to 'https://git.heroku.com/komo-service.git'