> was this via a generic L3 proxy, or did you mean something in AMQP-land?

This was in the past when the latest version of AMQP was 0.8, RabbitMQ didn't support TLS and Amazon Web Services didn't offer VPC, we were tunneling over SSLv3 from EC2 to our datacenter with stunnel in our DMZ.  We saw that on disconnect either the client or server side of the proxy would go stale and hold a connection, or would timeout on inactivity and drop both connections.

At that time, the client we used wasn't negotiating heartbeats.  To identify whether that was the root cause of stunnel's behavior, we had to run with and without heartbeats in a lab environment.