I am having the same issue: I kill a session but it stays on. The user has actually uinstalled the app that they had initiated the session from, and they are already connected on another app (whose session I can see since then). How is it possible?
They are connecting from an Android phone, so I presume that there is no possibility that the old uninstalled app is still running? I am not an Android person.
About 5 min later, after many unsuccessful attempts, suddenly the session clears from the server and a messages begin to come across the new session.