Unity 2D Android app runs well in editor but not on devices or emulators

I am developing an Android game with Unity 2D, build 2018.3 personal edition. I have set base Android version to 14 and target version to latest.

There are two scenes and Admob plugin installed. The game runs well in the Unity editor, but not on real devices or emulators.

When launching the app in device, a black screen pops up and closes immediately. The whole process happens in just 1 or 2 seconds.

Any help id aappreciated.