Troubleshooting

If you have problems you can try:

Running Clean in Xcode.
Deleting Xcode's derived data.
Removing node_modules then reinstalling dependencies. (rm -rf node_modules && yarn)
Clearing watchman's watches. (watchman watch-del-all)
Clearing React Native's packager cache. (react-native start --reset-cache)
Clearing React Native's iOS build folder. (rm -rf ios/build)