I'm not sure why this problem does not occur in Rails 4.2.5's development environment however, when running EpicEditor in Rails' production environment, it seems as though Rails cannot resolve the module's name to the expected EpicEditor:
/Users/mcneelyp/.rvm/gems/ruby-2.2.1/gems/actionpack-4.2.5/lib/abstract_controller/helpers.rb:162:in 'rescue in block in modules_for_helpers': Couldn't find Epiceditor::ApplicationHelper, expected it to be defined in helpers/epiceditor/application_helper.rb (NameError)
Either renaming the module to Epiceditor or renaming folders, files, and their references to epic_editor seems to fix this issue.