Although students and teachers can write a new Conversation message between the course end date and the section end date, they cannot reply to a message.  I believe this problem started when this issue was fixed: Soft-Concluded Courses allow for Students to Reply to Conversations. - Instructure Community (canvas...

Prior to this fix, it was a problem that students could reply to teachers after the section end date and teachers couldn't reply back, and the solution is to prevent students from replying after the course concludes, matching the teacher experience.  Great!  But our courses don't conclude until the section end date, which is some time after the course end date. Section end date overrides course end date, and full communication should be allowed until then.  Students can still submit assignments, teachers grade.

End of semester is coming up and I know many teachers and students are going to panic when the Reply button disappears from the Inbox.  It doesn't really make sense to me that they can write a new message but can't reply.  I hope this is just a tweak to the programming.  This should be considered "unwanted behavior".  Engineers, if I have to write an idea I will.