I reached out to our CSM as well because this affected our faculty teaching online in our Winter session. I was provided the following information:
We're aware of the issue with the Discussions Checkpoint feature release impacting Canvas' Speed Grader, and I apologize for the inconvenience this may have already caused. I am following that community thread as well. Our product and technical support teams are working on a resolution, and we'll keep you updated as soon as we have more information. In the meantime, as you mentioned, a Support case is helpful in getting things fixed too.
If you can get the faculty who are struggling to share their experiences directly with Instructure through a Case. While we can communicate in the community, the support tickets might have more merit based on volume. Just a thought.