connection not fully closed

We have been using Qpid C++ 1.39.0 broker/client for quite a while and recently start to encounter some error. The exact repro steps are not clear yet, but it seems more often under resource stress like more concurrent jobs or queue limit exceeded (as shown below). When it happens, we usually see a few things (may or may not happen together).

1. "[Broker] error Channel exception: session-busy: Session already attached"
2. "[Protocol] error Connection qpid.127.0.0.1:5672-127.0.0.1:xxxxx timed out: closing" (note, we use loopback address)
3. "[Broker] ... resource-limit-exceeded"
4. "[Client] error session-busy: Session detached by peer"
5. a few client TCP sockets left in CLOSE-WAIT state
6. for the same client, its CPU goes to 100%, strace shows nothing while gdb attach shows call stack around "Send --> waitForCapacity"

Your help in trouble-shooting is highly appreciated, thank you!