Does anybody have splashscreen appearing in app deployed on Amazon Fire?

I just added an Amazon Fire tablet to my collection of physical devices for testing. Everything seems to work fine, other than the splash screen does not appear (if it does, it vanishes before the human eye can see it). Has anybody else tested an app with a splashscreen on Amazon Fire? If so, how did you get it to work? The code I am using for my launcher activity is below, based on a sample somebody else published a while back.

Many thanks,

John H.

using System.Threading;
using System.Threading.Tasks;

using Android;
using Android.App;
using Android.Content;
using Android.Content.PM;
using Android.Views;
using Android.OS;

using Xamarin.Forms.Platform.Android;

namespace MarvinPrototype.Droid
{
    [Activity(
    ConfigurationChanges = ConfigChanges.Orientation | ConfigChanges.ScreenSize,
    Icon = "@drawable/icon",
    Label = "MarvinPrototype",
    LaunchMode = LaunchMode.SingleInstance,
    MainLauncher = true,
    NoHistory = true,
    ScreenOrientation = ScreenOrientation.FullSensor,
    Theme = "@style/Theme.Splash",
    WindowSoftInputMode = SoftInput.AdjustPan)]
    public class LaunchActivity : Activity
    {
        protected override void OnCreate(Bundle savedInstanceState)
        {
            base.OnCreate(savedInstanceState);
            System.Threading.Thread.Sleep(3000);
            StartActivity(typeof(MainActivity));
        }
    }
}