[doc][debugging] add known issues for hangs (vllm-project#6816)

docs/source/getting_started/debugging.rst

@@ -65,6 +65,10 @@ Here are some common issues that can cause hangs:
 
 If the problem persists, feel free to `open an issue on GitHub <https://github.com/vllm-project/vllm/issues/new/choose>`_, with a detailed description of the issue, your environment, and the logs.
 
+Some known issues:
+
+- In ``v0.5.2``, ``v0.5.3``, and ``v0.5.3.post1``, there is a bug caused by `zmq <https://github.com/zeromq/pyzmq/issues/2000>`_ , which can cause hangs at a low probability (once in about 20 times, depending on the machine configuration). The solution is to upgrade to the latest version of ``vllm`` to include the `fix <https://github.com/vllm-project/vllm/pull/6759>`_ .
+
 .. warning::
 
     After you find the root cause and solve the issue, remember to turn off all the debugging environment variables defined above, or simply start a new shell to avoid being affected by the debugging settings. If you don't do this, the system might be slow because many debugging functionalities are turned on.