APM network access forcing reboot to the F5 box

-- We have F5 unit in HA. From F5-APM network access has been published so that end user can get IP from trusted IP range. Then from that specific range end user can access Intranet resources. Whenever end user connecting to APM Portal and click at Network Access tab my F5 units falls back to Standby. We can see in logs after click at Network Access tab, F5 unit is changing state to standby. End user doesn't get IP from IP Lease pool. When we are testing same at standalone test F5 APM box, we are not facing same issue.