AWS S3 GetObjectAsync挂起/超时

official documentation 要从S3存储桶获取文本文件并挂起,请执行以下操作:

static async Task ReadObjectDataAsync()
{
    string responseBody = "";
    try
    {
        GetObjectRequest request = new GetObjectRequest
        {
            BucketName = bucketName,
            Key = keyName
        };
        //THIS NEXT LINE HANGS!!!!
        using (GetObjectResponse response = await client.GetObjectAsync(request)) 
        using (Stream responseStream = response.ResponseStream)
        using (StreamReader reader = new StreamReader(responseStream))
        {
            string title = response.Metadata["x-amz-meta-title"];