For a better explanation check this issue. The issue has been closed with this fix, but the fix creates another issue which is still open.
react-native-track-player uses foreground service in android to display a notification on with buttons to play/pause audio. However, the issue I am facing is that when I kill the app, the service is killed only the first time. After that if I open the App again, and play an audio, it doesn't stop after app kill and the audio keeps playing.