For an Assignment task type component, a 'Complete By' date must be set when creating this component in Programme Builder via Classic. This date serves as the due date for the task. Without this date, the system cannot auto-create the associated task. The component can only be marked as complete once the task has been created and completed.
Further details can be found at: FAQ: Why is an Assignment Task still showing as “Not Started” when evidence has been submitted by the Learner?