[release] Add GLM5 known issue for 2-node PD mixed deployment (#7436)

### What this PR does / why we need it?
Documented an issue in the 2-node PD mixed deployment scenario where
inference may hang when concurrency exceeds 8.(GLM5)

Noted that the issue has been fixed in PR:
- #7235 
- #7290.
---------
Signed-off-by: MrZ20 <2609716663@qq.com>
Signed-off-by: Mengqing Cao <cmq0113@163.com>
Co-authored-by: Mengqing Cao <cmq0113@163.com>

docs/source/user_guide/release_notes.md

@@ -51,7 +51,8 @@ This is the first release candidate of v0.17.0 for vLLM Ascend. Please follow th
 
 - GLM5 requires transformers==5.2.0, and this will resolved by [vllm-project/vllm#30566](https://github.com/vllm-project/vllm/pull/30566), will not included in v0.17.0.
 - There is a precision issue with Qwen3-Next due to the changed tp weight split method. Will fix it in next release.
-- The minimum number of tokens of prefix cache hit in hybrid model is 2k now
+- The minimum number of tokens of prefix cache hit in hybrid model is large now. The exact number is related to tp size, e.g., with tp 2, the block_size is adjusted to 2048, which means that any prefix shorter than 2048 will never be cached.
+- GLM5 has an issue in the 2-node PD mixed deployment scenario where inference may hang when concurrency exceeds 8 (fixed in PR [#7235](https://github.com/vllm-project/vllm-ascend/pull/7235) [#7290](https://github.com/vllm-project/vllm-ascend/pull/7290)).
 
 ## v0.16.0rc1 - 2026.03.09