In theory, your configuration seems completely normal, current and should work.
First, everything should work with udpreceive, without using CNMAT compatibility mode. If the IanniX partition is complex, IanniX may send too many messages, which saturate the network (example: a cursor = 50 messages / sec, so 10 cursors, 500 messages, etc.).
Then, when you say “broadcasting” do you use broadcast IPs (like 192.168.0.255) or unicast IPs? Perhaps to be able to help you, could you send me by email (firstname.lastname@example.org) your files (IanniX partition and Max patches)?
For the second question, I am not sure I understand: when you edit the message of a cursor and save the partition, the message is not saved? Or, would you like to create an OSC message “preset” to assign to each new cursor you instantiate?
Hope you are also safe and healthy during this period!