I had what may have been the same issue with a 2002 V70 - normally aspirated engine. I picked the car up off lease with 30,000 miles, certified with 100K Volvo warranty. We found that under full throttle, there was a puff of smoke out the rear (Q would have been proud).

I bought the car to take kids to schools 750 miles away, and was particularly concerned with breaking down hundreds of miles from home.

It was to the dealer several times to diagnose, and the dealer could not find the problem. I even insisted they do a compression check (all cylinders good). Eventually I was away for a week and dropped the car with the dealer, told them they had it for the week, and I expected it fixed. They found an unplugged hole on the back side of the engine; they said it was where the turbo oil return line goes. They said the same block is used on both engines. They never answered the question; why was this not plugged?