Troubleshooting IKEv2 on 10.11 El Capitan How do I troubleshoot IKEv2 VPN issues on El Capitan?

I've followed these instructions to create an IKEv2 VPN (and certificate) on a Ubuntu server that I want to connect to, which all seems pretty reasonable. 

I'm now trying to connect to it from my Mac. 
I've created an IKEv2 connection with (what I think are) the appropriate details. When I click connect, the VPN menu icon just shows the connecting lights for 2 minutes but nothing happens. There is no output (error or otherwise) in /var/log/system.log or on syslog -w. There is no error message or evidence of any sort of connection attempt on the server. If I change the server address in the VPN config to something non existent, the results are identical, so clearly it's not really doing anything useful. 

How do I find out what it actually thinks it's doing though? Surely something should be getting logged somewhere. I have tried adding 

log debug;
path logfile "/var/log/racoon.log";


to /etc/racoon/racoon.conf and restarting but I still get nothing.  

Update - I'm now getting some error output (post reboot):

Oct 12 21:27:06 testing nesessionmanager[519] &lt;Notice&gt;: NESMIKEv2VPNSession[VPN (IKEv2):930E0F86-1878-42E5-9CBD-08FD10677429]: Received a start command from SystemUIServer[415]
Oct 12 21:27:06 testing nesessionmanager[519] &lt;Notice&gt;: NESMIKEv2VPNSession[VPN (IKEv2):930E0F86-1878-42E5-9CBD-08FD10677429]: status changed to connecting
Oct 12 21:27:06 testing nesessionmanager[519] &lt;Error&gt;: Failed to find the VPN app for plugin type com.apple.neplugin.IKEv2
...
Oct 12 21:29:06 testing nesessionmanager[519] &lt;Notice&gt;: NESMIKEv2VPNSession[VPN (IKEv2):930E0F86-1878-42E5-9CBD-08FD10677429]: status changed to disconnecting
Oct 12 21:29:06 testing nesessionmanager[519] &lt;Notice&gt;: NESMIKEv2VPNSession[VPN (IKEv2):930E0F86-1878-42E5-9CBD-08FD10677429]: status changed to disconnected, last stop reason Tunnel did not come up in time
Now that I've found the error string, it looks like this is actually missing from the release. Perhaps it wasn't ready to ship.

https://forums.developer.apple.com/thread/18197

http://www.openradar.appspot.com/22735440