Puma caught this error: uninitialized constant ActionText::Engine::ApplicationController (NameError)

Question

開発環境

source 'https://rubygems.org'
git_source(:github) { |repo| "https://github.com/#{repo}.git" }

ruby '2.6.5'

# Bundle edge Rails instead: gem 'rails', github: 'rails/rails'
gem 'rails', '~> 6.0.0'
# Use mysql as the database for Active Record
gem 'mysql2', '0.5.3'
# Use Puma as the app server
gem 'puma', '~> 3.11'
# Use SCSS for stylesheets
gem 'sass-rails', '~> 5'
# Transpile app-like JavaScript. Read more: https://github.com/rails/webpacker
gem 'webpacker', '~> 4.0'
# Turbolinks makes navigating your web application faster. Read more: https://github.com/turbolinks/turbolinks
gem 'turbolinks', '~> 5'
# Build JSON APIs with ease. Read more: https://github.com/rails/jbuilder
gem 'jbuilder', '~> 2.7'
# Use Redis adapter to run Action Cable in production
# gem 'redis', '~> 4.0'
# Use Active Model has_secure_password
# gem 'bcrypt', '~> 3.1.7'

# Use Active Storage variant
# gem 'image_processing', '~> 1.2'

# Reduces boot times through caching; required in config/boot.rb
gem 'bootsnap', '>= 1.4.2', require: false

group :development, :test do
  # Call 'byebug' anywhere in the code to stop execution and get a debugger console
  gem 'byebug', platforms: [:mri, :mingw, :x64_mingw]
end

group :development do
  # Access an interactive console on exception pages or by calling 'console' anywhere in the code.
  gem 'web-console', '>= 3.3.0'
  gem 'listen', '>= 3.0.5', '< 3.2'
  # Spring speeds up development by keeping your application running in the background. Read more: https://github.com/rails/spring
  gem 'spring'
  gem 'spring-watcher-listen', '~> 2.0.0'
end

group :test do
  # Adds support for Capybara system testing and selenium driver
  gem 'capybara', '>= 2.15'
  gem 'selenium-webdriver'
  # Easy installation and use of web drivers to run system tests with browsers
  gem 'webdrivers'
end

# Windows does not include zoneinfo files, so bundle the tzinfo-data gem
gem 'tzinfo-data', platforms: [:mingw, :mswin, :x64_mingw, :jruby]
gem 'pry-rails'
gem 'active_hash'
gem 'devise'
gem 'ransack'

前提・実現したいこと

・エラーを解決したい/元のエラー画面に戻したい
学生情報と企業情報を一覧で見れるサイトを作成しています。
作成するにあたり、localhost:3000にてindex.htmlの画面を表示したいのですが、表示形式がおかしいエラーになります。こちらの解決方法（パソコンを再起動し、再度ログインする）を試してみましたがエラーは変わらず表示されています。

発生している問題・エラーメッセージ

Puma caught this error: uninitialized constant ActionText::Engine::ApplicationController (NameError)
/Users/muramatsusho/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/actiontext-6.0.4.1/lib/action_text/engine.rb:47:in `block (2 levels) in <class:Engine>'
/Users/muramatsusho/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/activesupport-6.0.4.1/lib/active_support/callbacks.rb:428:in `instance_exec'
/Users/muramatsusho/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/activesupport-6.0.4.1/lib/active_support/callbacks.rb:428:in `block in make_lambda'
/Users/muramatsusho/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/activesupport-6.0.4.1/lib/active_support/callbacks.rb:200:in `block (2 levels) in halting'
/Users/muramatsusho/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/activesupport-6.0.4.1/lib/active_support/callbacks.rb:605:in `block (2 levels) in default_terminator'
/Users/muramatsusho/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/activesupport-6.0.4.1/lib/active_support/callbacks.rb:604:in `catch'
/Users/muramatsusho/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/activesupport-6.0.4.1/lib/active_support/callbacks.rb:604:in `block in default_terminator'
/Users/muramatsusho/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/activesupport-6.0.4.1/lib/active_support/callbacks.rb:201:in `block in halting'
/Users/muramatsusho/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/activesupport-6.0.4.1/lib/active_support/callbacks.rb:513:in `block in invoke_before'
/Users/muramatsusho/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/activesupport-6.0.4.1/lib/active_support/callbacks.rb:513:in `each'
/Users/muramatsusho/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/activesupport-6.0.4.1/lib/active_support/callbacks.rb:513:in `invoke_before'
/Users/muramatsusho/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/activesupport-6.0.4.1/lib/active_support/callbacks.rb:134:in `run_callbacks'
/Users/muramatsusho/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/activesupport-6.0.4.1/lib/active_support/execution_wrapper.rb:119:in `complete!'
/Users/muramatsusho/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/activesupport-6.0.4.1/lib/active_support/execution_wrapper.rb:76:in `ensure in block in run!'
/Users/muramatsusho/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/activesupport-6.0.4.1/lib/active_support/execution_wrapper.rb:76:in `block in run!'
/Users/muramatsusho/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/activesupport-6.0.4.1/lib/active_support/execution_wrapper.rb:70:in `tap'
/Users/muramatsusho/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/activesupport-6.0.4.1/lib/active_support/execution_wrapper.rb:70:in `run!'
/Users/muramatsusho/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/actionpack-6.0.4.1/lib/action_dispatch/middleware/executor.rb:12:in `call'
/Users/muramatsusho/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/actionpack-6.0.4.1/lib/action_dispatch/middleware/static.rb:126:in `call'
/Users/muramatsusho/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/rack-2.2.3/lib/rack/sendfile.rb:110:in `call'
/Users/muramatsusho/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/actionpack-6.0.4.1/lib/action_dispatch/middleware/host_authorization.rb:82:in `call'
/Users/muramatsusho/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/webpacker-4.3.0/lib/webpacker/dev_server_proxy.rb:23:in `perform_request'
/Users/muramatsusho/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/rack-proxy-0.7.0/lib/rack/proxy.rb:63:in `call'
/Users/muramatsusho/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/railties-6.0.4.1/lib/rails/engine.rb:527:in `call'
/Users/muramatsusho/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/puma-3.12.6/lib/puma/configuration.rb:227:in `call'
/Users/muramatsusho/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/puma-3.12.6/lib/puma/server.rb:706:in `handle_request'
/Users/muramatsusho/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/puma-3.12.6/lib/puma/server.rb:476:in `process_client'
/Users/muramatsusho/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/puma-3.12.6/lib/puma/server.rb:334:in `block in run'
/Users/muramatsusho/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/puma-3.12.6/lib/puma/thread_pool.rb:135:in `block in spawn_thread'

該当のソースコード

routes.rb
Rails.application.routes.draw do
  root to: 'student_users#index'
  devise_for :student_users
  resources :student_users do
    collection do
      get 'search'
    end
  end
  devise_for :corp_users
  resources :corp_users, only: [:show, :index] do 
    collection do
      get 'search'
    end
  end
end

application_record.rb

class ApplicationRecord < ActiveRecord::Base
  self.abstract_class = true
end

corp_users_controller.rb(企業側コントローラー)

class CorpUsersController < ApplicationController
  before_action :search_corp, only: [:index, :search]
  before_action :move_to_index, except: [:index, :search]


  def index
    @corp_user = CorpUser.all.order("created_at DESC")
  end

  def show
    @corp_user = CorpUser.find(params[:id])
  end

  def search
    @results = @p.result
  end

  private
  def search_corp
    @p = CorpUser.ransack(params[:q])
  end

  def move_to_index
    unless student_user_signed_in? || corp_user_signed_in?
      redirect_to action: :index
      flash[:alert] = "ログイン/新規登録をして下さい"
    end
  end
end

student_users_controller(学生側コントローラー)

class StudentUsersController < ApplicationController
  before_action :set_student, only: [:edit, :show]
  before_action :move_to_index, except: [:index, :search]
  before_action :search_student, only: [:index, :search]

  def index
    @students = StudentUser.order("created_at DESC")
  end

  def new
    @student = StudentUser.new
  end

  def create
    StudentUser.create(student_params)
  end

  def show
    @student = current_student_user
  end

  def edit
  end

  def update
    student = StudentUser.find(params[:id])
    student.update(student_params)
  end

  def destroy
    student = StudentUser.find(params[:id])
    student.destroy
  end

  def search
    @results = @p.result
  end

  private
  def student_params
    params.require(:student).permit(:name, :college_name, :gakubu_name, :gakka_name, :one_word, :exp_occ, :circle_name, :qual_name,
                                    :intern_history_id, :graduation_id, :prefecture_id, :industry_id, :gender_id, :grade_id, :sales_amount)
  end

  def set_student
    @student = StudentUser.find(params[:id])
  end

  def move_to_index
    unless student_user_signed_in? || corp_user_signed_in?
      redirect_to action: :index
      flash[:alert] = "ログイン/新規登録をして下さい"
    end
  end

  def search_student
    @p = StudentUser.ransack(params[:q])
  end
end

試したこと

・コードを動いていた時のコードまで戻した
・ 前提・実現で書かれた解決方法を試した

補足情報（FW/ツールのバージョンなど）

初めはルーティングエラーになっていまして、こちらの記事を参考にapplication_record.rbを変更した後にこちらのエラー表示になりました。（コードを戻してもエラーになります）