I used to be able to message people in Groups in Inbox. Today when I tried to, I tried to chose a person but it said No Results. Why is that? Is it possible for a teacher to disable it? Or for a group to "expire?"
Did a term or quarter recently end at your school? There is no setting for an instructor to disable messaging from within Groups, but if the course the groups were within had end dates which passed that could have caused it. That is just a guess though; I don't know why else it would have changed.