In my case this particular problem happened when I was trying to archive a 0.40+ react-native app for iOS (solution was found here: Reliable build on ^0.39.2
fails when upgrading to ^0.40.0
).
What happened was that Xcode was trying to build the react-native libraries in parallel and was building libraries with implicit react dependencies before actually building the react library.
The solution in my case was to:
Disable the parallel builds:
Add react as a project dependecy