这个问题可能是因为异步上传部分方法在等待完成时出现了一些问题。为了解决这个问题，您可以检查以下两个方面：

1. 确保您的代码中正确使用了await关键字。
2. 检查您的上传部分方法是否正确实现了异步操作。

以下是示例代码，演示了正确使用await关键字和正确实现异步操作的方法：

public async Task UploadPartAsync(string filePath)
{
    var client = new AmazonS3Client();

    var uploadPartRequest = new UploadPartRequest
    {
        BucketName = "example-bucket",
        Key = "example-object",
        UploadId = "example-upload-id",
        PartNumber = 1,
        InputStream = File.OpenRead(filePath),
        PartSize = 1024 * 1024,
    };

    var uploadPartResponse = await client.UploadPartAsync(uploadPartRequest);

    Console.WriteLine("Upload part complete.");
}