If no explicit route is configured for a router in the network corresponding to the IPMP interfaces, then one or more explicit host routes to target systems need to be configured for the IPMP probe-based detection to work as expected. Otherwise, probe detection can fail to detect the network failures.
Configure a host route.
# route add -host destination-IP gateway-IP -static
# route add -host 192.168.102.1 192.168.102.1 -static
Refer to Configuring Target Systems in System Administration Guide: IP Services for more information.