Simple question, but somehow the answer escapes me.
In moving to Rails 6 with Zeitwerk, I get:
Please, check the \"Autoloading and Reloading Constant
I ran into this same issue, and it turns out it was complaining about a folder name.
Adding this to application.rb may work for you:
application.rb
Rails.autoloaders.main.ignore(Rails.root.join('app/junkyard'))