When the HA link is disconnected or when the Active and Standby Edges fail to communicate with each other, both Edges assume the Active role. As a result, both Edges start responding to ARP requests on their LAN interfaces. This causes LAN traffic to be forwarded to both Edges, which could result in spanning tree loops on the LAN.
Typically, switches run the Spanning Tree Protocol to prevent loops in the network. In such a condition, the switch would block traffic to one or both Edges. This would cause a total loss of traffic through the Edge pair.