As a result of Apple's constant striving to increase annoyance security, modern versions of iOS block the sending of broadcast UDP packets. The supplied example program lanchat.bbc relies on broadcast packets to announce itself to other devices on your LAN that might also be running that program.
I can't do anything about that, but in a future update I will attempt to arrange that lanchat on iOS can still respond to messages sent by other (non-iOS) devices, but not initiate a chat session.
Does anybody actually use lanchat? I thought it might be quite a fun tool in a household with multiple connected devices (phones, tablets, laptops etc.) but I don't think anybody has ever reported using it. It runs in both BBC BASIC for Windows and BBC BASIC for SDL 2.0 and is supplied as an example program with both.