Hello dear wine friends
Have also experienced the same problem in the lower 'white wines' section. although the cooler has only been in operation for 1 year. I have also thought about what could be the cause of this. In the back wall area of the cooler there are suction elements, each of which is covered with an air filter. Over time, these become very dusty, which is why there is less air circulation. As a result, cooling is no longer optimally guaranteed. Use a hoover to remove the dust from the outside and the unit will work perfectly again. This should actually be listed in the operating instructions. But it is not!

Thank you very much for your helpful answers. I have tested all the options and the unit works most reliably at a distance of just under 15 cm.

I would increase the distance to 15 cm!

My wine cooler stands at 8 degrees without any problems. Distance to the wall approx. 10 cm. No problems