App doesn't start on Internal / Alpha Testing

I've just finished recreating my iOS App for Android and have just started Internal / Alpha Testing for the first time. I have passed the review (although I don't know why they need this for 'internal' testing) and have waited for a long time to get it ready for the testing via Google Play Store. Now, finally I can, downloaded it to my device but as soon as I pressed Open, the app won't start. It just flashes the screen and that's it.

I tested in Debug Mode in Android Studio before and after this without changing anything. It just worked fine.

I contacted Google, have talked over chats as well as emails, but nothing is helping. They gave me this link: https://support.google.com/googleplay/?p=agent_troubleshooter , not helping.

So, is there any way I can know the cause of this?? Any way to get some logs out of it? Is there any settings I might have done wrong to create .aab? (although I think Google Play console won't accept it if anything is wrong...)

Any help or clue to solve this issue will be greatly appreciated.