test_low_latency.py hangs with 64 GPUs while working fine with 32 GPUs

With latest code (commit: f0d34aa), test_low_latency.py hangs on 8 node (64 H100 GPUs) with `--num-experts 256`. However, it worked fine when I ran it on 4 nodes (32 H100 GPUs). When it hung, I saw following warning log on some nodes:

```
Allocating buffer size: 1908.410496 MB ...
WARNING: destroy() was not called before DeepEP buffer destruction, which can leak resources.
```