Firewall HA Failure

We have Fortinet 600E Firewall in High availability configuration. Recently we have configured our new Fortinet manager in high availability with VRRP setup because both Fortinet managers are in different subnet and in different Geo location.

After completing the Fortinet manager setup when I add my Fortinet Firewall in Fortinet manager (primary) everything looks good so in my next step I do a Failover of my Forti Manager and After Failover I notice out of my two one of the firewall show unreachable. I try to install a policy it fails. then I try to push the system configuration, now here when I try to push the system configuration a major issue notice that all my running traffic stop working and I am not able to access my firewalls. then when I take a console access to the firewall I notice my HA was break (On hardware also HA LED was off) both firewalls are in stand alone state. so I restart my first primary firewall and then my traffic became normal and the primary firewall shows primary but the second firewall became stand alone and show no HA configuration.

I need to understand where it goes wrong. why my firewall HA was break. Firewall HA is configured long time back and we tested firewall failovers many time before.

The only last change we done is push system configuration which triggers the firewall HA Failure