F5-LC Active-Standby connected to Fortinet ACTIVE-ACTIVE via Stacked Switches issue

Hi Fortinet/F5/Cisco Experts,

 

here is the setup(disregard interface 1.4 on F5),

 

F5-LC: active-standby using trunk (LACP) and Tagged and connected fullmesh to the switches Fortinet: active-active and not connected in full-mesh to the switches Stacked Switch with port channels facing F5

 

Fortinet 1 is connected to Switch1 and Fortinet 2 is connected to switch 2.

 

Scenario:

 

Host PC behind the fortinet can access the internet when F5-LC1 is active, but when we perform the failover, and F5-LC2 becomes active, some of the hosts have intermittent connections going to internet and come hosts cannot connect to the internet at all.

 

Question:

 

what configuration on switch and fortinet can be added given that fortinet is not connected in full mesh with the switch. Or is it really necessary to connect the fortinet in full mesh with the switch?

 

I cannot see any config issue with F5.