Zeppelin server can't receive "RUN_PARAGRAPH" message through websocket from web client

After starting Zeppelin server, we find Zeppelin no response when people click the run button on paragraph, especially when the paragraph is using python interpreter.

We used a debugger to attach to the problematic server. Through websocket, the message "RUN_PARAGRAPH" was sent from front-end but it's received by zeppelin server. But other messages, such as "PING", "LIST_NOTE", "GET_NOTE" can be well received.

And after rebooting the server, the "RUN_PARAGRAPH" message can be received as expected.

In our use case, people mainly depend on python interpreter and due to this issue, we have to reboot the server every week or half a week.

Please help to take a look and any idea or input is welcome.  We are OK to patch our 0.8.2 installation.

Thanks a lot.