This is a bug that will be fixed in an upcoming release. To resolve this, change your Version to a version that is > API 19.
https://bugzilla.xamarin.com/show_bug.cgi?id=56272
Otherwise upgrade to 15.3 in your Visual Studio Installer to receive this fix as it is included in Xamarin.Android 7.3.0.27 and above.
solved Downgrade the android version cause error [closed]