webpacker: Upgrading to 1.1 breaks

After running bundle update (and noticing that I went from 1.0 to 1.1), relaunching my server (locally), I have this error: Can't find application.js in /my_app/public/packs/manifest.json. Is webpack still compiling?

When specifying 1.0 in my gemfile, it works fine. When moving back to 1.1, error comes back.

I have a basic setup, similar to what you advise in the readme. Happy to invite one of the maintainer to our private repo.