Steps to reproduce:
1) Download the attached "UdpServer.zip" on a Windows machine, extract it, open in Visual Studio, build and launch UdpServer.exe.
2) Go to Command Line, and enter ipconfig.
3) Write down the IPv4 address of the machine.
4) Connect an iOS device to a IPv6 network.
5) Extract and open the attached project "TestClient.zip".
6) Open "Test" scene.
7) Click on the "UdpClientTest" object in the Hierarchy and edit the IP address in the Inspector to the IPv4 address of the Windows machine.
8) Build the project for iOS.
9) Deploy the project to a device via Xcode.

The app sends and receives data from the IPv4 server. If the device is connected to a IPv6 network the IEEndPoint gets corrupted with IL2Cpp. This issue doesn't appear if the project is built with Mono2x or a IPv4 network is used.