I copied several assignments from one class to another. The class to which I copied them has the "zero for missing assignments" late policy applied to the Grade Center. I adjusted the dates of the copied assignments for the new class. For some reason, even though the due date is weeks from now, the assignments all show zeros for the students' grades.
This likely happened because you copied the course with a past due date and then changed the date. A glitch will use the original due date first. Try changing the due date in the source course first, then copy into your course. This should circumvent the problem in the future.
For this assignment you can Set Default grade to blank, rather than changing them individually. Screenshots below!