L2TP/IPSEC VPN client from IPv6 Network doesn't work

Hi there

Have found the issue when roaming client used notebook in LTE network can’t connect VPN server.

Configuration perfectly works in pure IPv4 network and even cleint behind LTE mobile access point works fine.

But when client has only IPv6 address something went wrong during IPSec tunneling

charon[3454]: 04[IKE] <l2tp_remote_access|1> no matching CHILD_SA config found for 2a02:2378:11e8:13:a5a0:a15a:5577:11dd/128[udp/l2f] === 64:ff9b::5e2d:3b2e/128[udp/l2f]
charon-systemd[3454]: no matching CHILD_SA config found for 2a02:2378:11e8:13:a5a0:a15a:5577:11dd/128[udp/l2f] === 64:ff9b::5e2d:3b2e/128[udp/l2f]

VPN configuration as below

set vpn ipsec ike-group IKE-1 close-action 'none'
set vpn ipsec ike-group IKE-1 dead-peer-detection action 'clear'
set vpn ipsec ike-group IKE-1 dead-peer-detection interval '30'
set vpn ipsec ike-group IKE-1 dead-peer-detection timeout '60'
set vpn ipsec ike-group IKE-1 key-exchange 'ikev1'
set vpn ipsec ike-group IKE-1 lifetime '7600'
set vpn ipsec ike-group IKE-1 proposal 1000 dh-group '14'
set vpn ipsec ike-group IKE-1 proposal 1000 encryption 'aes256'
set vpn ipsec ike-group IKE-1 proposal 1000 hash 'sha256'
set vpn ipsec interface 'eth1'
set vpn ipsec log level '1'
set vpn ipsec log subsystem 'any'
set vpn ipsec log subsystem 'cfg'
set vpn l2tp remote-access authentication mode 'radius'
set vpn l2tp remote-access authentication protocols 'mschap-v2'
set vpn l2tp remote-access authentication radius server xxxxx.tld key xxxxxx
set vpn l2tp remote-access authentication radius source-address 'xxx.xxx.0.10'
set vpn l2tp remote-access client-ip-pool default-range-pool range 'xxx.xxx.0.104-xxx.xxx.0.125'
set vpn l2tp remote-access default-pool 'default-range-pool'
set vpn l2tp remote-access gateway-address 'xxx.xxx.255.0'
set vpn l2tp remote-access ipsec-settings authentication mode 'pre-shared-secret'
set vpn l2tp remote-access ipsec-settings authentication pre-shared-secret xxxxxx
set vpn l2tp remote-access ipsec-settings ike-lifetime '3600'
set vpn l2tp remote-access ipsec-settings lifetime '120'
set vpn l2tp remote-access name-server 'xxx.xxx.0.50'
set vpn l2tp remote-access outside-address 'xxx.xxx.59.46'
set vpn l2tp remote-access ppp-options disable-ccp
set vpn l2tp remote-access ppp-options lcp-echo-timeout '3600'
set vpn l2tp remote-access ppp-options mppe 'deny'