traffic in ssl vpn unexpectedly blocked

Hi, We use fortigate 201E (firmware 6.2.2) as vpn cervice.

Somtimes unexpectedly all traffic in vpn is blocked. And I need to reconnect to use vpn again.

I disable all security profiles for firewall rules related with vpn, but it doesn't help. For security reason we don't use split tunnel, so all traffic pass through fortigate.

Also I use FortiAnalyzer with all license and IoC, maybe it can be related?

I've looked at all logs and don't have any idea