There is way to see vpn connection drop

Greetings,

I am using Fortigate 90D, with 5.2.3ver,  and created 30 users.

from some reason when I notice that when more than 10+ users connected the connection is became unstable which means users experience disconnection.

I checked Auto Connect, Always Up (Keep Alive) and Never Logout Inactive Users

but issue is still persist.

I mange to see via Logs & Report > Event Log > VPN or User (User xxx succeeded in logout, or login)

There is any way to see which connection is dropped and the reason for that?

Also users stay logged on with new IP, could be because of Never Logout Inactive Users

Thanks in advance,

Kpax