Hi Rich,
So there were 2 issues, on the emulator as you suggested.
disabling "Use Shared Runtime" and "Use Fast Deployment?" worked fine with the test app.
But in our app, we had one more issue caused due to the version 4.2.2
ArcGIS Runtime 100.2.1 does not work with Xamarin Forms and Android 4.2.2
The fix for the above was to include this.
JavaSystem.LoadLibrary("runtimecore");//which did not work with version 8.
So the final fix was to do this.
if (Build.VERSION.SdkInt <= BuildVersionCodes.JellyBean)
JavaSystem.LoadLibrary("runtimecore"); // fix for the android version 4.2
Regards
Sandeep