WINUI3中调用GetThumbnailAsync(ThumbnailMode.PicturesView)返回空值/空引用异常的问题求助

各位大佬好！我刚从C# WebApp转过来做WINUI3的Windows应用，用的是VS2022。现在跟着Microsoft Learn的Simple Photo Editor示例复刻，但遇到了个小问题，卡了好一会儿了，麻烦大家给点思路~

具体情况是这样的：我调用await ImageFile.GetThumbnailAsync(ThumbnailMode.PicturesView)时，返回的thumbnail一直是空值。但换成ThumbnailMode.DocumentsView就能正常拿到低分辨率的缩略图，另外用GetImageSourceAsync加载完整图片也完全没问题，这就很困惑，我到底哪里没做对？

下面是我的相关代码：

ImageFileInfo.cs #

public class ImageFileInfo : INotifyPropertyChanged
{
    public ImageFileInfo(ImageProperties properties, StorageFile imageFile, string name, string type)
    {
        ImageProperties = properties;
        ImageName = name;
        ImageFileType = type;
        ImageFile = imageFile;

        var rating = (int)properties.Rating;
        var random = new Random();
        ImageRating = rating == 0 ? random.Next(1, 5) : rating;
    }

    public StorageFile ImageFile { get; }
    public ImageProperties ImageProperties { get; }

    public async Task<BitmapImage> GetImageSourceAsync()
    {
        using (IRandomAccessStream fileStream = await ImageFile.OpenReadAsync())
        {
            //create a bitmap to be the image source
            BitmapImage bitmapImage = new BitmapImage();
            bitmapImage.SetSource(fileStream);
            return bitmapImage;
        }
    }

    public async Task<BitmapImage> GetImageThumbnailAsync()
    {
        var thumbnail = await ImageFile.GetThumbnailAsync(ThumbnailMode.PicturesView); //ImageFile.GetThumbnailAsync(ThumbnailMode.PicturesView);
        // Create a bitmap to be the image source
        BitmapImage bitmapImage = new BitmapImage();
        bitmapImage.SetSource(thumbnail);
        thumbnail.Dispose();
        return bitmapImage;
    }
}

MainWindow.xaml.cs #

public sealed partial class MainWindow : Window
{
    public ObservableCollection<ImageFileInfo> Images { get; }= new ObservableCollection<ImageFileInfo>();

    public MainWindow()
    {
        this.InitializeComponent();
        GetItemsAsync();
    }

    private async Task GetItemsAsync()
    {
        StorageFolder appInstalledFolder = Package.Current.InstalledLocation;
        StorageFolder picturesFolder = await appInstalledFolder.GetFolderAsync("Assets\\Samples");
        var result = picturesFolder.CreateFileQueryWithOptions(new QueryOptions());
        IReadOnlyList<StorageFile> imageFiles = await result.GetFilesAsync();

        foreach(StorageFile file in imageFiles)
        {
            Images.Add(await LoadImageInfoAsync(file));
        }
        ImageGridView.ItemsSource = Images;
    }

    public async static Task<ImageFileInfo> LoadImageInfoAsync(StorageFile file)
    {
        var properties = await file.Properties.GetImagePropertiesAsync();
        ImageFileInfo info = new(properties, file, file.DisplayName, file.DisplayType);
        return info;
    }

    private void ImageGridView_ContainerContentChanging(ListViewBase sender, ContainerContentChangingEventArgs args)
    {
        if (args.InRecycleQueue)
        {
            var templateRoot = args.ItemContainer.ContentTemplateRoot as Grid;
            var image = templateRoot.FindName("ItemImage") as Image;
            image.Source = null;
        }
        if(args.Phase == 0)
        {
            args.RegisterUpdateCallback(ShowImage);
            args.Handled = true;
        }
    }

    private async void ShowImage(ListViewBase sender, ContainerContentChangingEventArgs args)
    {
        if(args.Phase == 1)
        {
            var templateRoot = args.ItemContainer.ContentTemplateRoot as Grid;
            var image = templateRoot.FindName("ItemImage") as Image;
            var item = args.Item as ImageFileInfo;
            image.Source = await item.GetImageThumbnailAsync();
        }
    }
}

备注：内容来源于stack exchange，提问作者Charles de M.