创建外壳磁贴图像问题

我正在尝试使用 xaml 控件和可写位图创建图像。我会说大约 95% 的时间它在应用程序运行时运行良好，并且尚未看到它在计划任务中失败。当它失败时，它创建的图像是奇怪的。所有元素都对齐左上角，背景为黑色（颜色应为PhoneAccentBrush）。我已经尝试了很多方法来解决这个问题，但我迷路了。我可以复制该问题的唯一方法是不调用测量和安排。下面是代码，有什么想法吗？

Deployment.Current.Dispatcher.BeginInvoke(() =>
{
    TileHelper.UpdateFlipTile(this.LiveTile, this.Facility, this.METARs[0]);
});
public static void UpdateFlipTile(ShellTile shellTile, Facility facility, METAR metar)
{
    /*removed some variables to shorten code*/
    WriteableBitmap mediumImage = TileHelper.CreateMediumTileImage(facility.Description, metar.flight_category, wind, TileHelper.GetUri(metar), temp, metar.observation_time);
    SaveImage(mediumImageFileName, mediumImage);            
    FlipTileData flipTile = new FlipTileData()
    {
        Title = "",
        BackTitle = "",
        BackContent = "",
        WideBackContent = "",
        BackgroundImage = new Uri("isostore:/Shared/ShellContent/" + siteNumberEncoded + ".jpg", UriKind.Absolute)
    };
        shellTile.Update(flipTile);
    }
}
private static WriteableBitmap CreateMediumTileImage(string airport, string flightCategory, string wind, Uri imageUri, string temp, string lastUpdated)
{
    MediumMetarTile tile = new MediumMetarTile(airport.ToLower(), wind, flightCategory, temp, lastUpdated, imageUri);           
    tile.Measure(new Size(336, 336));
    tile.Arrange(new Rect(0, 0, 336, 336));
    WriteableBitmap image = new WriteableBitmap(336, 336);
    image.Render(tile, null);
    image.Invalidate();
    System.Diagnostics.Debugger.Log(0, "TileHelper.CreateMediumTileImage", "medium tile image created");
    return image;
}