Warning:
  Recently, the Flutter team has received several reports
  from developers indicating they are experiencing app
  crashes on certain devices on Android 6.0. If you are targeting
  Android 6.0, use the following steps:

If you build an App Bundle
Edit android/gradle.properties and add the flag:
android.bundle.enableUncompressedNativeLibs=false.

If you build an APK
Make sure android/app/src/AndroidManifest.xml
doesn’t set android:extractNativeLibs=false
in the <application> tag.

For more information, see the public issue.

Build an app bundle