React - Native IOS/Android Simulator problems

I’m currently building my first app with React - Native and I’m running into problems with both, IOS and Android Simulator. As I’m running the IOS Simulator with npm run ios, everything works out fine and the simulator starts successfully. But when I edit the App.js, the changes I made are not displayed in the simulator, I’m also not able to reload it using cmd+R. There is no error message displayed, it just doesn’t work.
The other problem occurs while trying to run the Android Emulator using npm run android. Trying this always leads to the following error message:

npm ERR! errno 1
npm ERR! feedIt@0.0.1 android: react-native run-android
npm ERR! Exit status 1
npm ERR!
npm ERR! Failed at the feedIt@0.0.1 android script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

npm ERR! A complete log of this run can be found in:
npm ERR! /Users/maurice/.npm/_logs/2020-07-12T21_53_06_596Z-debug.log
Maurices-MacBook-Air:feedIt maurice$

I tried fixing It, but I don’t know why these errors occur and hope for any help!