问4024 ErrOffGoBack 偏移量回退是什么错误？

通过PythonSDK在4G环境下并发上传6个文件，经常会出现2-3个文件发生4024错误，而其他的文件上传成功，是什么原因导致的呢,该如何解决？使用的是文件分片上传，分片大小默认值和64K都试过，每个文件大小5M左右。代码如下：def upload(lFile, rFile): result = cos.upload_slice(lFile, 'testbucket', rFile, slice_size= 64 * 1024) print("%s秒" % (timeit.default_timer() - start)) print(result)threads = []for file in files: thread = threading.Thread(target=upload, args=(file0, file1)) threads.append(thread)for thread in threads: thread.start()for thread in threads: thread.join()Log如下：84.7146229744秒{'message': u'\u504f\u79fb\u91cf\u56de\u9000\uff0c\u8bf7\u91cd\u8bd5', 'code': -4024, 'data': {}, 'httpcode': 400}156.596047878秒{'message': u'\u504f\u79fb\u91cf\u56de\u9000\uff0c\u8bf7\u91cd\u8bd5', 'code': -4024, 'data': {}, 'httpcode': 400}159.68591094秒{u'message': u'\u6210\u529f', u'code': 0, u'data': {u'url': u'http://web.file.myqcloud.com/files/v1/pic/primitive/PIC00002/005.jpg', u'access_url': u'http://testbucket-10002033.file.myqcloud.com/pic/primitive/PIC00002/005.jpg', u'resource_path': u'/pic/primitive/PIC00002/005.jpg', u'source_url': u'http://testbucket-10002033.cos.myqcloud.com/pic/primitive/PIC00002/005.jpg'}, 'httpcode': 200}159.959156036秒{u'message': u'\u6210\u529f', u'code': 0, u'data': {u'url': u'http://web.file.myqcloud.com/files/v1/pic/primitive/PIC00002/001.jpg', u'access_url': u'http://testbucket-10002033.file.myqcloud.com/pic/primitive/PIC00002/001.jpg', u'resource_path': u'/pic/primitive/PIC00002/001.jpg', u'source_url': u'http://testbucket-10002033.cos.myqcloud.com/pic/primitive/PIC00002/001.jpg'}, 'httpcode': 200}162.189401865秒{u'message': u'\u6210\u529f', u'code': 0, u'data': {u'url': u'http://web.file.myqcloud.com/files/v1/pic/primitive/PIC00002/004.jpg', u'access_url': u'http://testbucket-10002033.file.myqcloud.com/pic/primitive/PIC00002/004.jpg', u'resource_path': u'/pic/primitive/PIC00002/004.jpg', u'source_url': u'http://testbucket-10002033.cos.myqcloud.com/pic/primitive/PIC00002/004.jpg'}, 'httpcode': 200}192.324213028秒{u'message': u'\u6210\u529f', u'code': 0, u'data': {u'url': u'http://web.file.myqcloud.com/files/v1/pic/primitive/PIC00002/006.jpg', u'access_url': u'http://testbucket-10002033.file.myqcloud.com/pic/primitive/PIC00002/006.jpg', u'resource_path': u'/pic/primitive/PIC00002/006.jpg', u'source_url': u'http://testbucket-10002033.cos.myqcloud.com/pic/primitive/PIC00002/006.jpg'}, 'httpcode': 200}