I think you may be right. The device's actual ip address is 192.0.0.1, but this is outside the normal range of reserved local ip addresses. Perhaps this is confusing iOS and making it want to use the cellular radio to talk to the device instead of going over wifi.

Thank you!!! I've felt like a lone crazy person for years advocating against unit testing. In my experience they very rarely (or actually never) catch bugs, cost a lot of time to maintain, and also create ugly architecture. The obsession with number of lines of code covered is especially awful. Save unit testing for tricky algorithms, leave it out of simple view/model interactions!