A simple check but are you using Ethernet1 or Ethernet2 on the mac. Artnet doesn't always play nice on Ethernet2.

Try reducing the subnet of your Artnet down to 255.255.255.0 instead of 255.0.0.0. Just make sure that the first three octets are the same IE 2.0.0.x.

This is good practice anyway just to simplify the ethernet data.

Check and make sure that the Artnet network is not connected to a router that might mistake the 2.x.x.x network as something public that should be routed. One of the bad designs of the Artnet specification was the use of the 2.x.x.x public class A network. You can use 10.x.x.x and I usually do and set all my Artnet devices to some subnet of 10.x.x.x because its a non-routing subnet. However, this tends to freak many people out who are accustomed to their devices remaining in the 2.x.x.x.

Also remember that universe 1-4 of subnet 1 are also occupied by the Local Machine's Catalyst app.