I user Rails 4 and Cocoon gem. In fact, I know the problem - cocoon.js is not compiled into application.js as I can see in the browser. I do require cocoon in application.js and have the gem installed.
I do not use turbolinks. What else might cause this?
I got this answer from the developer of cocoon.
Good news! Tips for the future: do not do
rake assets:precompile
in development, because I have noticed weird effects with that too. And to really clean the assets, you have to dorake assets:clobber
(clean leaves the last three compilations and deletes the older ones).
I hope it helps.