Firebase Realtime Database concurrent connections reliability
Solution 1:
firebaser here
Do you have security rules on the concurrent path that require the user to be authenticated by any chance? Because there's an open issue around that, which has been causing problems for more people recently.
Aside from that we haven't seen reliability issues in onDisconnect handling recently, so we'd need to see more information about the lingering connections (a stand-alone repro would be good).