Do you use routed or bridged VPN? What’s your VPN network address?
Possible solutions are:
Enable "Push all static routes” in advanced options of roadwarrior settings on Nethserver.
If your Nethserver is not directly connected to www, meaning there’s a router in front of the Nethserver, you may need to configure a route (static route) on the router because the router does not know about the VPN network and drops the packets.
The static route should route the VPN network to the Nethserver.