I've also had this problem on a legacy project. It's a bundler 1.17.3 / ruby 2.4 / rails 4.2.11.3 and it was driving me up the wall.
The following nasty hack worked:
Gemfile:
gem 'rails-deprecated_sanitizer'
gem 'prototype-rails', git: 'https://github.com/rails/prototype-rails.git', branch: '4.2'
but that wasn't enough. I then had to get rails-deprecated_sanitizer to appear where the gems wanted it.
So in my project, I created lib/action_view/vendor/html-scanner.rb:
require 'rails-deprecated_sanitizer'
require 'rails/deprecated_sanitizer/railtie'
require 'rails/deprecated_sanitizer/html-scanner'
(I doubt all three are needed, mind)
This depends on lib being in your load paths of course.
That fixed the problem, and I was finally able to reset the db and launch the server.