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For further readers: restarting nginx can sometimes help. At least it did for me. 

Login to the server via ssh (web terminal doesn't work when websockets don't work)
Run the following command. This will restart nginx
/etc/rc.d/rc.nginx restart  
Or if you don't have ssh access somehow (I haven't tested this, but this is an idea)
Use the `user scripts` plugin and create a script with the command above.
Run the script, and it'll restart nginx, hopefully fixing websockets
 
Edit: hahaha I just saw that I was the original poster years ago! 😂