[Doc] Add Qwen3.5 fused MC2 known issue for 0.18.0 release (#8378)

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Signed-off-by: 李少鹏 <lishaopeng21@huawei.com>

docs/source/tutorials/models/Qwen3.5-397B-A17B.md

@@ -599,3 +599,8 @@ vllm bench serve --model Eco-Tech/Qwen3.5-397B-A17B-w8a8-mtp --dataset-name rand
 ```
 
 After about several minutes, you can get the performance evaluation result.
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+## Qwen3.5-397B-A17B Known issues
+
+- Issue1: For single-node deployment scenario, when fused_mc2 is enabled, using multi-DP model deployment may cause garbled or empty outputs after the model triggers recomputation.When tuning performance by adjusting model parallelism, ensure that this fused operator is disabled when DP > 1. For PD deployment scenario，D nodes can avoid this problem by enabling the recompute scheduler.
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