C＃Task.WaitAll不在等待

我的目的是从Amazon Web Services存储桶下载图像。

我有以下代码功能，可一次下载多个图像：

public static void DownloadFilesFromAWS(string bucketName, List<string> imageNames)
{
    int batchSize = 50;
    int maxDownloadMilliseconds = 10000;

    List<Task> tasks = new List<Task>();

    for (int i = 0; i < imageNames.Count; i++)
    {
        string imageName = imageNames[i];
        Task task = Task.Run(() => GetFile(bucketName, imageName));
        tasks.Add(task);
        if (tasks.Count > 0 && tasks.Count % batchSize == 0)
        {
            Task.WaitAll(tasks.ToArray(), maxDownloadMilliseconds);//wait to download
            tasks.Clear();
        }
    }

    //if there are any left, wait for them
    Task.WaitAll(tasks.ToArray(), maxDownloadMilliseconds);
}

private static void GetFile(string bucketName, string filename)
{
    try
    {
        using (AmazonS3Client awsClient = new AmazonS3Client(Amazon.RegionEndpoint.EUWest1))
        {
            string key = Path.GetFileName(filename);

            GetObjectRequest getObjectRequest = new GetObjectRequest() {
                 BucketName = bucketName,
                    Key = key
            };

            using (GetObjectResponse response = awsClient.GetObject(getObjectRequest))
            {
                string directory = Path.GetDirectoryName(filename);
                if (!Directory.Exists(directory))
                {
                    Directory.CreateDirectory(directory);
                }

                if (!File.Exists(filename))
                {
                    response.WriteResponseStreamToFile(filename);
                }
            }
        }
    }
    catch (AmazonS3Exception amazonS3Exception)
    {
        if (amazonS3Exception.ErrorCode == "NoSuchKey")
        {
            return;
        }
        if (amazonS3Exception.ErrorCode != null && (amazonS3Exception.ErrorCode.Equals("InvalidAccessKeyId") || amazonS3Exception.ErrorCode.Equals("InvalidSecurity")))
        {
            // Log AWS invalid credentials
            throw new ApplicationException("AWS Invalid Credentials");
        }
        else
        {
            // Log generic AWS exception
            throw new ApplicationException("AWS Exception: " + amazonS3Exception.Message);
        }
    }
    catch
    {
        //
    }
}

图像的下载全部正常，但Task.WaitAll似乎可以忽略，其余代码继续执行-这意味着我尝试获取当前不存在的文件（因为尚未下载）。

我找到了另一个问题的答案，这个问题似乎与我的相同。我尝试使用答案来更改我的代码，但它仍然不会等待所有文件下载。

谁能告诉我我要去哪里错了？