I had to remove rack-cache to figure out why articles index page did not display all articles when a user clicked on a tag to get related articles.
First remove the rack-cache gem, delete rack-cache gem in Gemfile and run bundle. To troubleshoot this problem, in production.rb set:
config.assets.compile = true
In your development machine (not production) run:
bundle exec rake assets:precompile returned 1 instead of one of 
This gave a clue that there was a reference to rack-cache in application.rb.
rake assets:precompile --trace RAILS_ENV=production
** Invoke assets:precompile (first_time)
** Invoke assets:environment (first_time)
** Execute assets:environment
** Invoke environment (first_time)
** Execute environment
LoadError: cannot load such file -- rack/cache Be sure to add rack-cache to your Gemfile
config.action_dispatch.rack_cache = true from application.rb
Redeploy the code and from rails console production in the production machine, run:
to clear the cache. The problem turned out to be not related to rack-cache. At least one of the suspect has been ruled out. I temporarily disabled the find related articles by tag.