The crux of the issue seems to be a topology that fails to rebuild after an interruption of network services. It is relatively easy to reproduce, though not sure how common the issue would be in practice. General reproducer instructions: 1. Set up a 2-node broker cluster (reproducer is replicated with network pinger) using wildcard addresses for the acceptors, fully-qualified hostnames for the cluster connectors and fully-qualified hostnames for the network ping targets. configure live broker host with 1 source of DNS information (e.g. DNS server) configure backup broker host with 2 sources of DNS information (2 DNS servers or DNS + hosts) configure network pinger with 2 hosts - I used the 2 DNS servers 2. Start the brokers and wait for them to settle and replicate initially 3. Stop the source of DNS information for the master broker (I stopped the DNS service, leaving the host up) 4. Wait for master broker to start logging UnknownHostException errors 5. Interrupt the connection between live and backup broker. I did this by temporarily disabling the relevant interface on the live node with the attached network-interrupt.sh script. 6. Observer both brokers are live 7. Restart DNS service 8. Both brokers remain live 9. Restart backup broker 10. Backup fails to reconnect, and topologies for both brokers show zero nodes and zero members. Issue seems to be that master loses the topology information and fails to rebuild it, so acceptor used for CORE fails to transmit topology to slave and slave cannot reconnect.