A friend who does automotive testing and base level system debugging for several large car manufacturers said this is one of the problems he’s been involved in trying to rectify. Of the many things he has been looking at, coasting is seems to be a large contributor to the symptoms. One symptom of coasting is the fuel system allows a small amount of fuel to exit through the combustion chambers unburnt and may be adding to the PPF clogging issue. (unconfirmed yet) While this may not cure the issue by simply turning the function off he does suggest that the manufacturer may have the same opinion with their advice on in gear deceleration as part of the regen process advised to customers. In no way am I suggesting this is a fix as it was just a conversation over coffee and cake, but as it can’t do any harm it’s got to be worth a try.
The Hybrid 230 doen’t seem to suffer the issue and you have to turn coasting on in the menu if you want to use, which judging by the forums not many do as it means driving in eco mode.
The problem relates mainly with the ICE and MHEV 🙂