I had the same problem. Change the DNS server (resolv.conf) to be your router so the VPN client can find the VPN server when the network bounces.
I had the problem intermittently; I think the problem was whether the cache was stale. Setting resolv.conf to 192.168.1.1 (your router/gateway) fixed the problem.
BTW, Debian 9 so far appears to be more stable with the VPN client than Debian 7.
Sent from my MS Surface