ace-rails-ap was added in #11625 at version 3, but the latest is 4. It has some changes to precompilation, so the worker files are automatically precompiled.

The precompilation list (config/environments/production.rb) ought to be tidied at the same time, as many of the files being precompiled probably aren't needed as they're required into the main app.js via vendor/javascripts/vendor.js instead.