Packet loss problem with Edgemax Lite routers and Draytek Routers (IPSec VPNs)

We have multiple Edgemax Lites (Ubiquiti) routers and Draytek routers. They are all connected via IPSec site-to-site VPN tunnels.

Although the tunnels are up and running we are regularly experiencing packet loss. This is causing quite a lot of problems because the sites all use an application called AniTa Terminal Emulator, which runs on port 23, crashes because of connection trouble.

I have posted packet captures etc. to the Ubiquiti forum without luck:

http://community.ubnt.com/t5/EdgeMAX/VPN-IPsec-Packet-Loss/m-p/625113#U625113

I'd be happy swapping to OpenVPN with OSPF but the Drayteks don't seem to support being an openvpn client.

Thanks,

Danny