Forticlient disconnects from the VPN after around a minute

I had forticlient SSL VPN v4 in windows 10. Everything worked great until one day the VPN started to disconnect after a minute or so. I think what I did is installing forticlient app from windows 10 store (which didn't work btw, but that might be because of the fortiOS in the fortigate).

The error I got is:

The user SYSTEM dialed a connection named fortissl which has terminated. The reason code returned on termination is 630.

I uninstalled v4 and I installed latest forticlient SSL VPN (5.4) and when I dial the VPN it connects successfully (as before), but after about a minute the VPN disconnects.

Now the event viewer in "Application" under the source "RasClient" says:

The user SYSTEM dialed a connection named fortissl which has terminated. The reason code returned on termination is 829.

Any ideas anyone? I am working on this for 3 days without any luck...

Thanks!