求助：客户端偶发[E1008]Reached timeout

**问题描述**
客户端偶发出现 `[E1008]Reached timeout=15000ms`，从 rpcz 抓到的trace看，服务端很快进行了response，但是不知道什么原因客户端一直没有收到，其中一个trace如下

```
09:38:09.066607 . 0 Requesting xxxxx baidu_std log_id=0 call_id=146673133403889 trace=d2a8ed1019254ce4 span=d2a8ed1019254ce4
09:38:09.066624 . 17 Requested(3581) [1]
09:38:24.066684 15. 60 [E1008]Reached timeout=15000ms @xxxx:8060
09:38:24.066710 . 26 Enter user's done

2024/04/22-09:38:09.067145 Received request(3581) from xxxx:35494 baidu_std log_id=0 trace=d2a8ed1019254ce4 span=d2a8ed1019254ce4
09:38:09.067176 . 31 Processing the request in a new bthread
09:38:09.067241 . 65 Enter xxxxx
09:38:09.067395 . 154 Leave xxxxx
09:38:09.067407 . 12 Responded(32)
```

按照 [server_debugging](https://github.com/apache/brpc/blob/master/docs/cn/server_debugging.md)对客户端和服务端进行了排查
* bthread_worker_usage 很低 (但依然尝试增加 brpc_concurrency，没有效果)
* 机器的CPU、IO和网络流量都不高

请问下有没有其它可能的原因或排查手段呢

**Versions (各种版本)**
brpc: 1.3.0

Start by reading docs/cn/server_debugging.md and comparing the client and server rpcz traces shown for brpc 1.3.0, including the bthread_worker_usage observation. The issue names no source entry point or test; completion would require identifying a reproducible cause or documenting a concrete diagnostic path.

Written by the indexing model from the issue text.