A. The meeting is a channel meeting and not all the students are a member of that meeting. B. Same as A with channel meeting, except they are joining via web / anonymous with the link in an e-mail / calendar invite. C. There are meeting policies setup and applied differently to different students and some of the students are not allow chat? D. Students are joining with web client and not signed in / using desktop client and not signing in and chat is restricted from external users via policy?