I think it could be anything that someone wants to be better at. Everyone has different problems to work on. Communication might not be any problem for one group and to them a bad communication could be non functional if they see it in someone else. But that same group could have a problem with anger at each over something and another group might see that as being non functional. It could also I think mean something outside of a group like not being able to speak with anyone or not being able to leave the house, but people who aren't plural have things like that to deal with too. I guess I'm really saying that I don't think there's a single one answer because it is probably a personal issue that every group would decide for themselves. I hope I made some sense.

-Butterfly