The ventilation in the housing unit is not optimal.

Check the ventilation cutouts (1), (2), (3) (see figure).
If necessary, remove objects that obstruct the ventilation. Remove any dust.
The ventilation cutouts must each be at least 31"2 (200 cm2) in size. The air must be able to rise freely behind the refrigeration appliance.
To check the installation, contact your dealer or Miele Service.