I have a Miele built-in freezer which is about 6 years old. In the last 3 months it has developed an annoying habit of failing to cool properly. I’ve noticed that the upper drawers seem warmer than the lower ones. Emptying the freezer and fully defrosting seemed to sort it previously but then the problem recurs. Its presently only reaching -9 deg C.
There is a tear in the door seal (about 4 inches long) but this doesn’t seem to affect the magnetic part creating a good seal.
No model number but sounds like a frost free cabinet torn door seal will pull in outside air and will cause evaporator to clog with ice allowing inside temp to rise or poss. fault not defrosting due to defrost timer defrost stats defrost heater???
Check your hand book to see if there is a cooling fan and or filter for it. Slow air flow across the condensing coils will cause this fault, could be blocked/restricted with fluff/dog hair etc.