Isn’t it possible to run an Art-Net sending application on the same computer (or more correctly network interface) as Notch is running?
Using GMA3 onPC with Command Wing connected, set to broadcast on the loopback interface produces the error message in Notch: Failed to init Artnet: Cannot find ip 127.0.0.1. This is sort of expected, but the error message does not appear when using the network interface (with a 192.168.x.x address) - although there is still no activity in Notch (now the Art-Net monitor reports "No Artnet data received in 20 seconds).
Checked the signal with Artnetominator which shows ArtNet activity on used channels, so there should be a valid signal on the port.
Checked value mapping with MadMapper that behaved as expected.
Also checked offsets in both GMA and Notch to check for varying interpretations of starting addresses without it making any difference.
A HW loopback using two network interfaces works, but it is quite fiddly to set up.