I understand this is a quite old thread, but I have combated exactly the same situation before, and in my case the network configuration was the culprit.
For some reason, the initiator has sent its messages from one IP address, but another IP has been opened to accept incoming replies (and this second IP has been specified in target’s route).
I have detected this by accident, really. When I tried to end conversation on the target side, it hasn’t closed, but the EndDialog message appeared in sys.transmission_queue with the status:
Connection attempt failed with error: ‘10060(A connection attempt
failed because the connected party did not properly respond after a
period of time, or established connection failed because connected
host has failed to respond.)’.
I have no idea why the target restart has triggered the breakdown, but when network engineers have fixed the issue and I changed the target’s route, everything flew to their destinations as it was supposed from the start.