Without more details I'm afraid I can only try to help you troubleshoot. Post as much code as you can. The route, the controller action, the view it's rendering, and any relevant logs from localhost and heroku would be a great start.
I've had Heroku requests timeout on my rails apps many times - in development there is often no time limit but if your request is taking too long that definitely could be the issue. How long does the request take on development? It could be as simple as shaving off a few seconds.
Otherwise I would say to check this out:
Heroku websocket connection
Also be sure to clear everything you can on your browser, try other browsers, incognito mode, all of that. Try to isolate the problem to one area - even though Heroku is throwing the error it is almost certainly not causing the error.
Check your routes. Look at everything that is happening with that request in your dev and prod logs and try and find something different about this request. Compare it to others.
It is also a good idea to understand your logs and increase their verbosity -
https://devcenter.heroku.com/articles/logging
What levels of logging are available for Heroku?
Good luck!