This is not a fault.
To add laundry, proceed as follows:
Open the door.
Add or remove laundry.
Close the door.
Touch the Start/Add laundry sensor control.
ADD is shown on the display of the washing machine/washer-dryer/tumble dryer.
To add laundry, proceed as follows:
Open the door.
Add or remove laundry.
Close the door.
Touch the Start/Add laundry sensor control.