If it joined once by accident it shouldn't still show up in the server list. Once it was removed or turned off Hangfire would remove it from the list after not seeing a heartbeat for a period of time.
Does the QA server listed in production have a heartbeat?
Does the QA server listed in production have the same server name, port, and hash (mouse over name) as the QA server in QA?
My guess is there must be a 5th instance of your setup deployed somewhere (QA server pointing to production) and that's the one showing up.