Native module cannot be null, but the app works fine - react-native

react-native run-ios successfully builds the project and the app is started at simulator, however, I got the error below, I tried to get more details in the Xcode log, I only got this:
[fatal][tid:com.facebook.react.ExceptionsManagerQueue] Unhandled JS Exception: Native module cannot be null.
How can I debug this error? is it just a warning? I can see fatal in Xcode log.
If I press on Dismiss in simulator, the error below gone and the app seems to work fine..
Any idea?

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Understanding "Application has not been registered" error

I've been given a new React Native app to maintain and whenever I build it or run it in the simulator, I get the "Application has not been registered" error. There are no other errors in the console before this message (although there are some warnings). I can't find any code issues as if the error message is dismissed in the simulator, the app runs fine so the bundler is running correctly, although on an actual device, this registers as a crash on open.
I'm running in the simulator using react-native run-ios from the project root. Builds for running on actual devices is managed by Fastlane.
My app doesn't make an explicit call AppRegistry.registerComponent due (I think) to the way react-native-navigation is set up, so most of the info online about this error doesn't apply.
Where should I go next to figure this out?

react native invalid hook call in release build

I tried to build my react native app and got the error below.
it works totally fine in debug build while app crashes in release build.
I got this by logging my android device with the command adb logcat '*:E'
Thanks in advance.

Unable to resolve module 'react-devtools-core' from 'node-modules/react-native/Libraries/Core/Devtools/setupDevtools.js'

Trying to debug react native iOS application but when I am running the app from xcode, getting this error.
'react-devtools-core' from 'node-modules/react-native/Libraries/Core/Devtools/setupDevtools.js'

SyntaxError: Attempted to redefine property 'marginTop'.

I have an error in my app when it's run in android emulator.
My app works perfectly in iOS, but when I tried to run in Android show this.
Why occurred this?

React Native App crashes if signed and released. Works fine in debug mode

React Native App crashes if signed and released. Works fine in debug mode. It doesn't throw any error in the screen. It simply crashes. When I looked at cat log. no error.
I also tried build apk with --info, but no additional info while crashing. I also tried building APK by setting minifyEnabled false.
When run the app in debug mode by connecting my phone via USB, it works.
I'm tried creating apk with --debug but I'm unable to install it my phone, it says parsing error when I try to install using app installer.
I got the following logcat errors. What does it mean?
09-03 11:03:07.968 W/ActivityManager(1344): Force finishing activity com.myapp/.MainActivity
09-03 11:03:08.012 W/BroadcastQueue(1344): Skipping deliver [background] BroadcastRecord{cb72147 u-1 android.net.conn.CONNECTIVITY_CHANGE} to ReceiverList{7bf2161 22421 com.myapp/10100/u0 remote:b9cdcc8}: process crashing
09-03 11:03:08.035 W/ActivityManager(1344): Dismiss app error dialog : com.myapp
09-03 11:03:13.095 I/WindowState(1344): WIN DEATH: Window{3f22c22 u0 /com.myapp.MainActivity}

I finally found the cause. There is module called react-native-material-design-searchbar which was causing the issue. The weird part is, if directly copy the SearchBar.js from that module and use it all works fine even in release, but if use module as direct import it's not working only in release mode. So weird. The SearchBar is good, so now I'm using directly by copying the file to my project.

I fixed this error by uninstalling uglifyjs and reinstalled the latest (using NPM).