That's an interesting case. We fixed something for 3.4.0 beta2 that could be related to this issue. We are releasing beta 2 today so let me know if you see the same issue with the new beta.
After stress testing on beta2, I did not activate the clustering on beta 2 yet.
During stress test when Dashboard shows 1000 Current Users, there are 380 unconnected sockets.
After stopping the stress test and waiting till the "Client Sessions" show no session.
there is only 1 unconnected socket.
I am going to activate the clustering next.