In 2017, I worked at a company that built a websocket based app and ran it on Heroku. We had this exact same problem and all 5 of the engineers at the time spen

In 2017, I worked at a company that built a websocket based app and ran it on Heroku. We had this exact same problem and all 5 of the engineers at the time spent all day until we realized that we had socket connections still connected to some "ghost dyno". I can't remember exactly what we did but I think we just kept deploying over and over again until the old one finally went away.