After further investigation, finally identified from the log that my app was killed by Android itself because the Android built-in process which my app used was crashed.
To resolve this, just need to request Android to restart my app when it is being killed. This will make the scan longer but at least the scan will at the end finish.
The scan notification which didn’t go away after the app is killed is probably another issue which hopefully can be solved…
Anyway you can get the latest version of the app from Google Play below.