There is a similar question here in which I identify troubleshooting steps. In fact, Firefox now ships within it’s dev tools the ability to see websocket messages (if there are any). Your suspicion about where the error is correct. Or at least it’s between you (the client browser) and the OOD server (apache).
You mention /var/log/ondemand-nginx, did you check the httpd24 logs as well? (the other user said there was nothing there, but maybe there is for you?).
Then just to be clear, and for documentation purposes, here’s what a successful connection looks like. Note the response code is 101 switching protocols.
