Update 2017-02-01: Users report that with OSX 10.12.3 shutting off IPv6 solves this connection issue.
OLD: This is broken on OSX due to changes in IPv6 and IPv4. Right now there is no solution to the Wi-Fi connection on Sierra that we're aware of, and we're waiting for Apple to do their work to unbreak this.
In the meantime, you've got options:
- Bluetooth (free, built into iPad Air and above), available since 1.7.3
- musicIO MIDI (lowest-latency, best professional solution for MIDI-over-USB-lightning cable... also, we are co-authors of the app)
- iConnect ($60+)
- midiMittr (free app)