Note, as of this time, only use the release build; other builds will not run or build correctly and may silently fail.
Make sure the local.properties has these:
Some issues might show up for iOS but not in Android, or vice versa.
When working with files, Android paths can be hard coded, but iOS paths change, so the path has to be concatenated appropriately on iOS.
Resolve some problems by simply removing the node_modules director and re-running npm-install.
Use the following command or apply to ~/.bashrc:
export ANDROID_HOME=$HOME/Android/Sdk
For debian 9 stretch see the following for more info:
When switching branches, remember to run a make clean or remove the ~/android/app/build folder entirely.
Remember building requires XCode and signing as a developer or with a team account. Set config in the .xcodeproj file with targets "idly" and "idlyTests".
Try toggling the Bluetooth manually on both devices.