Unable to view ipsec tunnel and ipsec monitor option in GUI when vpn connections are up

Dear All

Details

Fortigate Model : FGT 500E

FortiOS : 5.6.8

Unable to view Ipsec tunnel ( VPN-->IPSec tunnel) and IPSec monitor ( Monitor -->IPSec monitor) in Fortigate Web GUI when VPN connections are up. there is almost 800+ dial up site to site VPN is connecting at the same time. when we disconnect the internet and if the VPN tunnel is in down status we can view both IPSec tunnel and IPSec monitor option. 

I have killed httpsd process and also restart the fortigate firewall device. still same result. 

help plz

Regards

Mahesh