
GetTumbnailAsync sometimes returns NULL, which your code does not account for. Do this instead:
IAsyncOperation<BitmapImage> Photo::GetImageThumbnailAsync() const
{
auto thumbnail = co_await m_imageFile.GetThumbnailAsync(FileProperties::ThumbnailMode::PicturesView);
BitmapImage bitmapImage{};
// fix for when thumbnail is NULL
if (NULL != thumbnail)
{
bitmapImage.SetSource(thumbnail);
thumbnail.Close();
}
co_return bitmapImage;
}