This article explains an issue where FPC does not come online after the junOS upgrade in case of HA cluster.
During the minimal downtime HA cluster upgrade process, FPC for the secondary node will not come online after the upgrade, ksyncd process will crash and generate core files as shown below:
User@SRX> show system core-dumps
-rw-r--r-- 1 root wheel 8552448 Nov 29 01:40 /var/tmp/ksyncd_13545.core.1732833624.0
This issue is expected if the HA control links are not disconnected before initiating the minimal downtime junOS upgrade process. It is important to disconnect/disable all the HA cables before initiating the upgrade.