Hello @LindsayMcCabe
Thanks for Posting this in the Global canvas Community!
I was able to find THIS similar post where a Community member mentioned: "go to your outlook admin profile, search for the group created for your course. Usually it has the same name as the course in canvas. The change the group's privacy so it can receive messages from external sources. then retry to "add all class" feature in canvas." Have you checked this already?
Another Idea I had was trying to sync the integration data from the integrations tab in the course settings. HERE is the Canvas guide on that.
Let us know what you find out on this. Seems very odd!
-Colton