"arp" or "ip neigh" showing hardware MAC address as INCOMPLETE

Issue

• Losing network connectivity on gateway or router or firewall failover
• arp output getting Hardware address as (incomplete)

# arp -n
IP address       HW type     Flags       HW address            Mask     Device
10.0.0.245                              (incomplete)                     eth0
10.0.0.254       ether        c         00:21:d7:aa:bb:cc                eth0

• ip neighbour shows a MAC address as INCOMPLETE

# ip neigh
10.0.0.254 dev eth0 lladdr 00:21:d7:aa:bb:cc REACHABLE
10.0.0.245 dev eth0  INCOMPLETE

• Cannot see ARP Reply getting generated in the system after receiving the ARP Request from the source host.