FortiGate HA Upgrade - Route sync

Hi,

I'm troubleshooting a FortiGate HA setup connected to Cisco Nexus using OSPF/Gracefull restart/BFD.

Trying to near/sub-second downtime in a failover situation.

And I'm reading in a FortiNet document that there is a difference in a failover situation when doing an upgrade of the HA cluster.

It states that the routing table (kernel routes i assume) are not synced during the upgrade, which would lead to a more severe outage than a regular cluster failover.

Does anybody have more information/experience with this? I was under the impression that during the upgrades of the HA members the failovers would only start after synchronisation is complete.

Regards,

Jack