RT-AC66U VPN problem

[atr]

Asus RT-AC66U with firmware 3.0.0.4.374_979.

Symptom:

VPN server works ONLY right after VPN service restarts or router reset.

No matter windows or android VPN client can connect to AC66U VPN sever one time only. It will not work after the client is disconnected.

It seems that the VPN server stop running and refuse to respond any connection attempts. The status of the VPN server is "PPTP VPN Server- Running" anyway.

in order to make VPN client connects to the RT-AC66U:

1) Get vpn client ready
2) remote login the AC66U management page
3) disable the vpn server
4) enable the vpn server
5) repeatedly press the connect button of vpn client
6) VPN gets connected in few seconds after vpn sever restarted.

Is it normal?

ATR