Launching on IOS, sessions do not appear in the Session Frontend

Licensee reports:

Dug into this further and our iOS devices aren't receiving any of the handshake messages sent by the Session Frontend (or any other UDP messages for that matter) because multicast is failing to be configured for UdpMessageMulticastSocket:

1. 2018-10-08 17:32:10.449517+0100 Game[805:233267] [2018.10.08-16.32.10:449][ 0]LogTcpMessaging: Initializing TcpMessaging bridge
2. 2018-10-08 17:32:10.468145+0100 Game[805:233267] [2018.10.08-16.32.10:468][ 0]LogUdpMessaging: Initializing bridge on interface 0.0.0.0:0 to multicast group 230.0.0.1:6666.
3. 2018-10-08 17:32:22.330339+0100 Game[805:233267] [2018.10.08-16.32.22:330][ 0]LogIOS: FSocketSubsystemIOS::InternalBSDSocketFactory
4. 2018-10-08 17:32:30.315135+0100 Game[805:233267] [2018.10.08-16.32.30:314][ 0]FUdpSocketBuilder: Failed to configure multicast for UdpMessageMulticastSocket (loopback: 1, ttl: 1)

1. Create a new IOS project

2. Launch on an IOS device which is connected to the same LAN as the editor

3. Open Window | Developer Tools | Session Frontend

The session does not appear under "My Sessions"