When an instructor imports a course that has the Missing Policy enabled e.g., to award zeros for missing assignments AND does not use the functionality to adjust or remove due dates during the import process, all students currently in the course at the time of the import are immediately given zeros on assignments with a (past) due date and the instructor must remove the zeros so that, when the course is published, students don't see zeros for assignments that they haven't had a chance to complete.
There are several ways to address the issue, but I will propose that the Missing Policy functionality should be updated to prevent it from triggering in an unpublished Canvas site. This will provide a window of time for the instructor to import content into an unpublished course and update due dates prior to publishing to avoid the erroneous zeros from being automatically applied.
