Black screen with release build for Android

I am unity 2019.1.12f1. We have been working on a game from a year now. It was working fine. However, form last 5 days, we cannot build a release build with our key store. The app in android mobile gives a black screen or crashes.

We have tried building with proguard, minify and 32 bit display buffer (on and off). Our multithreading is off.

Do note that when creating new key, we are able to run the game properly. Also, debug build is running properly.

Kindly, help. I need to know if the keystore is corrupted or firebase, admob and manifest are creating a problem for us. It is urgent for us, as we are launching our game and a huge marketing campaign is going to run after a week.