When you schedule a closed day and send a notification to all affected clients, the Class Booking (Reservation) Cancelled by Staff client notification is sent. This notification is designed for canceled Classes, but when a closed day is added to the schedule, it is also sent for any canceled Appointments or Events. Some email and SMS variables will not populate for these service types.
To prevent this, when you are selecting which services should be canceled during a closed day, click Cancel only selected services and deselect all Appointments and Events. Once you have finished scheduling the closed day, you can cancel each Appointment and Event for that day from the schedule.