Lost route after some second after successfully logon to ssl vpn

Procedure (on ASG 8 with actual Version):
I’am establishing successfully a SSL VPN connection with the ssl Client. For a few seconds, I’am able to connect to the internal server. Then, the server is unreachable.
I’ve printed out the routing table during the vpn logon process. For a short time, there is a route like:
172.20.0.0 255.255.255.0 10.242.2.5 10.242.2.6
This line will gone after some seconds.

If I add the route again manually in the command line like:
>route add 172.20.0.0 mask 255.255.255.0 10.242.2.5
a connection to the server is possible.

After disconnect and reconnect the vpn connection. Same issue, I must add the route manually.

Any idea’s

Thanks for help.

Michael