Still it took me a day and a half to figure this out with the help of @Juriaan, and the fix is only so-so. I wish Isadora would have a more integrated way to use Artnet or DMX.
Mark here. I just wanted to say I'm sorry you faced this frustration. The implementation of ArtNet is relatively basic, and we haven't put loads of energy into it because we don't have a sense that ArtNet is important for the bulk of Isadora users. Given that we have limited resources, we have to focus our energy towards the items that are most valuable to the most people.
That said, @DusX on the team uses ArtNet frequently so he is a fan, and this means you have someone who will push for a better implementation on the team. From my side, I want to see every feature in Isadora be as easy and robust as possible, beause every capability Isadora offers is increases its overall value. Please continue to offer your feedback. I and the team are listening, and we can revisit what your requests Isadora Werkstatt and see what can be done.