Possible Ipsec Session Issue - Not sure where to troubleshoot issue next?

[Robert_White]

We recently updated our wireless access points to a controller based model. At the remote sites the AP's need to authenticate (ipsec) to the control plane. Initial configuration and reboots of the AP authenticate and work as expected. If my two Fortigates devices lose connectivity for a lengthy period of time the AP will not authenticate untill I reboot the remote Fortigate. I can ping everything prior to the reboot & nothing comes up blocked in the log from both sides. Any thoughts on what next steps should be?

High Level Overview:

Aruba 7010 -> Fortigate 200D (5.2.3) -> ENS (L2 Private Fiber) <- Fortigate 90D (5.2.3) <- Aruba IAP-215  

Thanks!