The ProxySG appliance is acting as a transparent load-balancer for an ADN deployment or has multiple ADN-concentrators in ADN/connection-forwarding cluster.
It can take up to 30 seconds to detect the failure of an 'accelerator' node (i.e. a concentrator in the load-balancing group).
Background Information: The ProxySG appliance (the ADN manager) checks for a heartbeat from all nodes in the ADN network every 15 seconds. If one is declared 'dead' by the ADN manager, the transparent load-balancer ProxySG appliance searches for an alternate node.