I would gues its been poorly re-mapped !.
If it goes well, doesnt missfire and isnt " too " heavy on fuel, then the map would be the only reason.
I had exactly the same with mine last year. Spent a whole summer trying to get to the bottom of it, injectors, wiring, turbo hoses.
Got he map taken off, and " bingo ", no more smoke.
You may have a delaminating turbo hose, but this usually would cause a loss of power at full " chat ".
Del.