While adding a redundant node to be a part of an HA pair for router redundancy, when the device comes online the routers work as individual routers or go into split brain.

+ while running 128status, it shows connectivity issues to second node or zookeeper might be started as standalone.

+ while running "show system connectivity", the other node is showing as "disconnected"

+ ping from shell fails to the sync interface ip of the other node

This above symptoms could lead to conclusion that basic connectivity for sync interface between the nodes is broken

+ Check if the relevant configuration for the sync interface is in place, validate the configuration manually.

# show running configuration flat | grep sync

+ Check if the sync interface is visible in Linux space and IP is assigned to interface

# ip a

+ Check the connectivity between the nodes by running a ping

# ping <IP of sync interface of other node>

If the interface is not visible in Linux space, then make sure configuration has forwarding set to false as below

# config authority router 128t-br1 node node1 device-interface SYNC forwarding     false