In release mode FCM_Token is not genterating.

Hello Guys ... I am facing issue a with this module. I have everything in place and it is working when I built the debug apk of the app or when I build it in the android emulator or in a physical device and the token is generating fine ... but when I build a release apk the token stops generating. I have tried everything and can't seem to find the issue ... What could be wrong here ?