Hi sharkkae,
Did you use the default websocket come with MAG?
In another case, I saw it's not compatible with a jetty websocket server(same symptom as your test), but after I replaced it with the tactical websocket assertion, it's working perfectly.
I believe the tactical websocket assertion is much up-to-date, and worth a try.
Please open a support ticket to ask for the tactical websocket assertion.
Regards,
Mark