In an environment with dual HA clusters (active/passive), connected through the same subnet to each each other, the ARP tables for the upstream routers display the same MAC for the different cluster IP addresses. Traffic is not passing through the LAN.
Resolution
The Group ID is part of the MAC address in a HA pair. Each pair of devices in a multi-cluster environment must have a unique Group ID in order to prevent duplicate MAC entries in upstream ARP tables. Changing the Group ID in one of these clusters should resolve the problem. The change must be performed on each device as HA management configurations do not sync to each other.