问上传到COS上的文件丢失？

偶发现象，我们应用在cos上上传的文件，当时是可以用的，但是过了一段时间后，有时文件会莫名其妙找不到，请问可能是什么原因？

报错原因如下：

```

Caused by: com.qcloud.cos.exception.CosServiceException: The specified key does not exist. (Status Code: 404; Error Code: NoSuchKey; Request ID: NWQ5MThhMmJfM2I0MzIyMDlfNTdlN18xYjNiZTFj); Trace ID: OGVmYzZiMmQzYjA2OWNhODk0NTRkMTBiOWVmMDAxODc0OWRkZjk0ZDM1NmI1M2E2MTRlY2MzZDhmNmI5MWI1OTdjMThiOTNjNGNkMmZlYjcxYWFjMTc4NTk2ZTg2Njg5NzI3MTJkNTNmMDRmZTMxZmE1MTA2OTkwYmEyZDliMTY=

at com.qcloud.cos.http.DefaultCosHttpClient.handlerErrorMessage(DefaultCosHttpClient.java:295)

at com.qcloud.cos.http.DefaultCosHttpClient.exeute(DefaultCosHttpClient.java:387)

at com.qcloud.cos.COSClient.invoke(COSClient.java:487)

at com.qcloud.cos.COSClient.getObject(COSClient.java:902)

at com.test.utils.ftp.CosUtils.download2Stream(CosUtils.java:171)

... 2 more

```