I found an issue when retrieving appointments using MultiDayView.GetAppointmentsInInterval
The issue occurs when creating a new appointment where AllDay is set to true
In the appointment, the Start and End date is automatically both set to the same value
When adding the appointment to the MultidayView and retrieving the appointments in interval (interval is set to 1 minute) the Appointment is not returned.
I guess the call only uses the Start and End date and not using the AllDay value