This seem to be necessary now if you use image assets in your project. Without executing the below command, my release android app variant won't show any required images 🤔
Paste this into your terminal, inside the project folder
react-native bundle --platform android --dev false --entry-file index.js --bundle-output android/app/src/main/assets/index.android.bundle --assets-dest android/app/src/main/res/