I have the same issue.

Hi Colonel,

The discussion section is not (yet) available on the subjects that have the new content experience rolled out on them already. The new content experience is limited to the math and science content right now, and will be rolled out in the following months to the other subjects. More updates are expected in the coming months, including adding discussions back.

This article can provide more information: https://support.khanacademy.org/hc/en-us/community/posts/7654483526925-Update-New-Assignments-and-Mastery-information-on-exercises-videos-and-articles-

I hope this helps! Please let me know if you have any further questions.

Similar issue is occurring with my brother.