[strongSwan] [KNL] received netlink error: No such file or directory (2) - unable to add SAD entry with SPI

[ck+strongswanusers at bl4ckb0x.de]

Hello!
I am trying to setup StrongSwan on a new Gentoo server.
My Lumia 950XL (Windows Phone 10) is the connecting device.

The connection fails, because I am getting "Invalid payload received" on 
the client side.

Debug Log: http://pastebin.com/huTE2PxY
Config: http://pastebin.com/9q84N6ii

If I am correct, the connection seems to work, authentication works, but 
somethings after the ip assigning fails?

15[IKE] scheduling reauthentication in 3405s
15[IKE] maximum IKE_SA lifetime 3585s
15[IKE] peer requested virtual IP %any
15[IKE] assigning virtual IP 192.168.185.1 to peer 'myuser'
15[IKE] peer requested virtual IP %any6
15[IKE] no virtual IP found for %any6 requested by 'myuser'
15[KNL] received netlink error: No such file or directory (2)
15[KNL] unable to add SAD entry with SPI cf2e6262
15[KNL] received netlink error: No such file or directory (2)
15[KNL] unable to add SAD entry with SPI c6e057aa
15[IKE] unable to install inbound and outbound IPsec SA (SAD) in kernel
15[IKE] failed to establish CHILD_SA, keeping IKE_SA

According [1], all modules are build into my kernel and available.

[1] https://wiki.strongswan.org/projects/strongswan/wiki/KernelModules

Any ideas? I've no idea, what could be else missing?

Cheers
Conrad