[Bug] [SFTP] 抽取速度变为0，并且任务一直不结束

### Search before asking

- [x] I had searched in the [issues](https://github.com/apache/seatunnel/issues?q=is%3Aissue+label%3A%22bug%22) and found no similar issues.

### What happened

我使用的seatunnel版本是2.3.9，json文件如上，任务跑着跑着速度就将为了0，任务一直处于运行状态，这种情况偶尔出现，不知道是什么原因导致的

### SeaTunnel Version

2.3.9

### SeaTunnel Config

```conf
{
"env" : {
"jobMode" : "BATCH",
"parallelism" : 1
},
"sink" : [
{
"data_save_mode" : "DROP_DATA",
"enable_header_write" : true,
"field_delimiter" : "\u0001",
"file_format_type" : "text",
"host" : "192.168.0.139",
"password" : "******",
"path" : "/tmp/seatunnel//iceberg_catl_test/78_TEST_BATCH_COMMON/20250430/000007/1745980859764",
"plugin_input" : "sftp_reader_output",
"plugin_name" : "SftpFile",
"port" : "22",
"tmp_path" : "/tmp/seatunnel/",
"user" : "root"
}
],
"source" : [
{
"field_delimiter" : "\u0001",
"file_format_type" : "text",
"host" : "192.168.0.159",
"password" : "******",
"path" : "/tmp/seatunnel//iceberg_catl_test/78_TEST_BATCH_COMMON/20250430/000007/1745979721170",
"plugin_name" : "SftpFile",
"plugin_output" : "sftp_reader_output",
"port" : "22",
"schema" : {
"fields" : {
"AGE" : "STRING",
"ID" : "STRING",
"NAME" : "STRING",
"SEX" : "STRING"
}
},
"skip_header_row_number" : 1,
"user" : "root"
}
],
"transform" : []
}
```

### Running Command

```shell
seatunnel --config sftp.json
```

### Error Exception

```log
没有异常信息，任务一直在运行，目前看最长的运行了20多个小时，但是从第一次出现速度为0开始，后面的速度就没有变过
```

### Zeta or Flink or Spark Version

zeta

### Java or Scala Version

_No response_

### Screenshots

_No response_

### Are you willing to submit PR?

- [ ] Yes I am willing to submit a PR!

### Code of Conduct

- [x] I agree to follow this project's [Code of Conduct](https://www.apache.org/foundation/policies/conduct)

The report names sftp.json and the `seatunnel --config sftp.json` entry point; start by reproducing the SFTPFile batch job with the shown SeaTunnel 2.3.9 and Zeta configuration. Observe the runtime state when throughput reaches zero; done means identifying why the job does not terminate and providing a verified fix or diagnostic result.

Written by the indexing model from the issue text.