The Canvas support team has a link on a users profile that "deletes the user's cache".
So far this has fixed issues when the items don't display on the course navigation or courses do not display in the Inbox to message.
We requested to have access to this magic tool as it clears the users Canvas cache which often is an issue. Let's vote it up that admins have access to it. I entered a ticket for our admin to have it but it was denied. :-(