Canvas has recently updated Discussions to include an option to disallow threaded replies. When enabled, students will not be able to reply to other students’ posts within a discussion.
This update may have affected some existing discussions due to differences in how new and legacy discussions are managed. As a result, Canvas may have automatically enabled the “Disallow Threaded Replies” setting to preexisting discussions.
As this time, we recommend checking the discussion settings in your active courses and master course shells to verify that the “Disallow Threaded Replies” option is not enabled for discussions where students need to reply to each other’s posts.
Below are screenshots illustrating how a discussion appears with threaded replies both disabled and enabled.