There may be multiple explanations. The two most common ones are:
1) The employee has an open case and continues to respond every other week.  Their wellbeing does not change immediately and as a result their responses still fall in the “red zone”. Since they already have an open case, which is waiting for a follow-up interview (which is typically 3-4 weeks ahead), no new case is set up.
2) Over the past 12-month period the employee has had 2 cases (which in some cases might be a maximum number of cases per year), and as a result no new cases are set up but are instead referred to the closest manager, HR or other healthcare service.