I am a teacher using Teams with my students, and have just started using Breakout rooms with them. All but one of the students is unable to use the chat function in the room, with an error message that it has been disabled by the administrator appearing for them. I am able to send announcements to the rooms.
I have not disabled this function - indeed, I can't find an option anywhere to enable or disable it - and have been unable to find any reason online as to why this would not be working.
Did the student, who is unable to participate in the chat, join the session in the normal way. E.g. did they have (Guest) after their name? We have had some feature appear as "disabled" if the user enters the session by accidentally bypassing the normal authentication - basically by joining the session via a link, going to the web browser and entering as a guest.