So I did another test with video, since that was working the last time, to verify if video works when using the second USB-ethernet port. In short; it doesn’t.
The longer answer;
When the miniMAD is “normally” connected to the network, using its main ethernet port, all OSC messages work, both from my laptop (sending the OSC messages over a network) or from the miniMAD itself;
# from my laptop
# from the minimad itself
Note that I’m using liblo-tools for testing, which lets me send OSC messages from the command line. To send messages from the miniMAD, I first ssh into it using ssh pi@MINIMAD.local
When I boot the miniMAD with only an ethernet connection on the secondary USB-ethernet port, it’s not responding to ANY OSC message (neither from my laptop nor from localhost; I can still ssh into it).
Interestingly, when I shortly connect the main ethernet port to a random raspberry pi that I have lying around (also when the miniMAD is already running and connected on only the secondary ethernet port), it will shortly display the “SYNCING” overlay message over the video after which the OSC messages suddenly work, even after I disconnect the ethernet cable from the main ethernet port and only leave the secondary ethernet port connected...
It seems like the networking part of the minimad software doesn't activate until a connection on the main ethernet port is detected?