Is webpack still compiling?
This blog post was originally published a little while ago. Please consider that it may no longer be relevant or even accurate.
I've just run into this issue using Rails Webpacker on Heroku in production. Everything was worked fine locally but once it was deployed the app just shutdown completely and Bugsnag filled up with these sort of errors.
Looking at the logs Webpacker was actually being run and all looked good under the hood, but for whatever reason the app wasn't happy. I narrowed down the issue to an NPM module - webpack-manifest-plugin. I had updated from v1.2.1 to v1.3.0 after which the app immediately broke. When rolling back to the previous version the app was fine.
I created a new blank Rails app that worked fine on Heroku with webpack-manifest-plugin@v1.3.0 so there's something funky going on here, but as a quick fix you can roll back and keep moving. Hopefully this issue will be fixed upstream, wherever it may be.
