Hi, I have my PERSONAL and UNPROVED opinion about the whole issue, based on some points.
1) Even without any official information, it seems that the engine head has changed from 1st March on; more specifically, some details of valves should have been changed.
2) I haven't seen any complaints of "hidden kangaroos" or of unepected stalls for vehicles delivered from April on (not only Ateca's, but also all other VAG models fitted with the 1.5 engine), so I think that the (possible) engine change was done to fix those issues (maybe among others).
3) Some (VAG) drivers reported that their dealers could check a "secret list" and say if their cars were affected or not.
4) Some (VAG) drivers reported a weird evolution of the issues: increasing up to 3000 miles, stable up to 6000 miles, decreasing (in some case: zeroing) after 6000 miles.
5) Some (VAG) drivers reported big improvements after using a valve lubrication additive.
6) The software update took several months to be developed, and it is available for MY19 only, MY18 drivers are still waiting for it.
Based on the above points, my PERSONAL and UNPROVED opinion (sorry to repeat it) is that such issues could be due to insufficient valve lubrication, depending on the complexity of the technical solutions applied to the 1.5 engine, in turn due to hardware problems affecting only some suppliers/lots.
Such insufficient valve lubrication could vary, from vehicle to vehicle, e.g. depending on different suppliers and/or supply lots.
The valve lubrication can vary as the mileage goes up (tear and wear of parts).
Hardware problems could have been fixed by changing the head for engines manufactured after 1st March.
IF all or some points above were true, this "theory" could explain why:
- some cars are affected and others (likely the most) are not (different hardware);
- some drivers reported big improvements from additives (improved lubrication);
- dealers can check a list and say if a specific car is affected or not (hardware list);
- some drivers reported an evolution of their problems as mileage increases (change of lubrication due to tear and wear);
- engines manufactured after 1st March seem not affected by any issue (hardware change);
- VAG engineers took months to develop the software update (which has to deal with an hardware problem) and this is now available only for MY19 (likely they need other months for MY18 due to different engine hardware).
Just my two pence....