Okay I just tried 5 Ghz with the phones and still offline ... But my Shield_TV is online via 5 Ghz...
So it seem to be a problem with the Mobile phones... Or some DHCP Problem...
But it worked like a Charme the last month... And since a few hours only the mobile phones are offline
You are right - it was a VPN problem.
My Shield_TV is routed over WAN, so they are connected to the internet...
My Phones are routed over VPN.
And killswitch worked the way it should: makes them offline when not connected to VPN...
I am sorry that I did not checked this at first...