Fortinet Failover

you may need to enable session-pickup in your HA configuration.

set session-pickup enable
set session-pickup-connectionless enable

On ipsec tunnels you may need to add
set ha-sync-esp-seqno enable

Do you mean traffic not passing when doing failback from secondary to primary?
Do you have BGP configured on FGT? If yes, routes are present after failback?

Verify connected switches has learnt the MAC of FGT in new switch port.
You can use below hatalk debugs to see the status of failover event and gratuitous ARP sent by FGT Primary(new master)

di de di
di de reset
di de app hatalk -1
di de console timestamp enable
di de en

(Run the above debugs on both devices and perform the failover failback activity)

First of all, how are you measuring those 2 and 30 sec? And how are you exactly simulating/triggering a fail-over and fail-back? 30 sec is generally the default delay timer if your switch port has port-fast disabled. Wondering if you're disconnecting the eth cable connected to a switch to simulate the primary failure. 

Toshi

Toshi