Q:

React app slows to a crawl only in developer mode

We have a React app. Lately we are experiencing an issue which only appears in "developer" mode. Two of the modules causes the app to become unresponsive for several seconds. The cpu works hard and memory usage spikes. If I change the settings in Webpack to "production" it works smoothly.
I have tried doing performance recordings in devtools, but I am unable to interpret anything useful from it.
I have tried making the Webpack configuration as simple as possible without any signs of improvement.
I am not posting any code since I don't really know where the issue(s) might be. But maybe someone can give some ideas about where to look or how we can pinpoint the issue.

A:

Thanks to @noitse for pinpointing the problem. I removed "redux-immutable-state-invariant" and that fixed the problem.

