[strongSwan] Stongswan 5.32 and Android client

[asterisk asterisk]

I have a home debian 8 linux server with strongswan installed. Wish to
have roadwarrior configured as below

config setup
    cachecrls=yes
    uniqueids=yes

conn ios
    keyexchange=ikev1
    authby=xauthpsk
    xauth=server
    left=%defaultroute
    leftsubnet=0.0.0.0/0
    leftfirewall=yes
    right=%any
    rightsubnet=10.1.2.0/24
    rightsourceip=10.1.2.0/24
    rightdns=4.2.2.1
    auto=add

It works when I use IPhone IOS to connect. However, when I want to use
Andriod phone to connect, it fails.

The linux server is behind an asus RT-66 router with NAT passthrough
configured and port forward UDP 50, 500, 4500.

If I put the linux server in a netgear router, it works with Android.

Any suggestion to this?