Added sample packaged project and added app context based on whether you are running the app natively or thru an app package

src/NotificationFlyout.Uwp.UI/Extensions/ExecutionMode.cs

@@ -0,0 +1,15 @@
+using Microsoft.Windows.Sdk;
+
+namespace NotificationFlyout.Uwp.UI.Extensions
+{
+    internal class ExecutionMode
+    {
+        internal static bool IsRunningWithIdentity()
+        {
+            uint packageNameLength = 0;
+            int result = PInvoke.GetCurrentPackageFullName(ref packageNameLength, "1024");
+
+            return result != 15700;
+        }
+    }
+}

src/NotificationFlyout.Uwp.UI/Extensions/ImageSourceExtensions.cs

@@ -4,18 +4,31 @@ using System.Drawing;
 using System.IO;
 using Windows.UI.Xaml.Media;
 using Windows.UI.Xaml.Media.Imaging;
+using System.Threading.Tasks;
+using System.Runtime.InteropServices;
+using System.Text;
 
 namespace NotificationFlyout.Uwp.UI.Extensions
 {
     public static class ImageSourceExtensions
     {
-        public static Icon ConvertToIcon(this ImageSource imageSource, uint dpi)
+        public static async Task<Icon> ConvertToIconAsync(this ImageSource imageSource, uint dpi)
         {
             var bitmapImage = (BitmapImage)imageSource;
-            var uri = $"{AppDomain.CurrentDomain.BaseDirectory}{bitmapImage.UriSour‌​ce}".Replace("ms-appx:///", "").Replace("/", "\\");
+            if (!ExecutionMode.IsRunningWithIdentity())
+            {
+                var uri = $"{AppDomain.CurrentDomain.BaseDirectory}{bitmapImage.UriSour‌​ce}".Replace("ms-appx:///", "").Replace("/", "\\");
 
-            using var stream = File.OpenRead(uri);
-            return new Icon(stream, new Size(PInvoke.GetSystemMetricsForDpi((int)SystemMetricFlag.SM_CXICON, dpi), PInvoke.GetSystemMetricsForDpi((int)SystemMetricFlag.SM_CYICON, dpi)));
+                using var stream = File.OpenRead(uri);
+                return new Icon(stream, new Size(PInvoke.GetSystemMetricsForDpi((int)SystemMetricFlag.SM_CXICON, dpi), PInvoke.GetSystemMetricsForDpi((int)SystemMetricFlag.SM_CYICON, dpi)));
+            }
+            else
+            {
+                var storageFile = await Windows.Storage.StorageFile.GetFileFromApplicationUriAsync(bitmapImage.UriSource);
+                using var stream = await storageFile.OpenStreamForReadAsync();
+                return new Icon(stream, new Size(PInvoke.GetSystemMetricsForDpi((int)SystemMetricFlag.SM_CXICON, dpi), PInvoke.GetSystemMetricsForDpi((int)SystemMetricFlag.SM_CYICON, dpi)));
+
+            } 
         }
 
         private enum SystemMetricFlag : int

src/NotificationFlyout.Uwp.UI/NativeMethods.txt

@@ -1 +1,2 @@
-GetSystemMetricsForDpi
+GetSystemMetricsForDpi
+GetCurrentPackageFullName

src/NotificationFlyout.Wpf.UI.Controls/NotificationFlyout/NotificationFlyoutXamlHost.cs

@@ -179,7 +179,7 @@ namespace NotificationFlyout.Wpf.UI.Controls
             }
         }
 
-        private void UpdateIcons()
+        private async void UpdateIcons()
         {
             if (!_isLoaded) return;
 
@@ -196,7 +196,7 @@ namespace NotificationFlyout.Wpf.UI.Controls
             var iconSource = _systemPersonalisationHelper.Theme == SystemTheme.Dark ? _defaultIconSource : _lightIconSource;
             if (iconSource == null) return;
 
-            using var icon = iconSource.ConvertToIcon(dpi);
+            using var icon = await iconSource.ConvertToIconAsync(dpi);
             _notificationIconHelper.SetIcon(icon.Handle);
         }
 
@@ -212,6 +212,7 @@ namespace NotificationFlyout.Wpf.UI.Controls
                 flyoutHost.RequestedTheme = requestedTheme;
             }
         }
+
         private void UpdateWindow()
         {
             if (!_isLoaded) return;