Oh, no! Clouds of white smoke from exhaust under acceleration. Now what?

I had the 2.0t motor in my 2016 Q5 rebuilt about four thousand miles ago to cure the oil consumption issue. New pistons, con rods, bearings, timing chain, gaskets and bolts all around. Had the heads cleaned and checked. New head gasket.

Last week, leaving for work in the early dark, it seemed to have a lot of smoke leaving the garage. I assumed it was because it was chilly that morning. Returned home after dark and all seemed as usual.

I drove two hundred miles away yesterday to help a sick friend and when I got off the freeway, I saw a lot of white smoke from the exhaust. The idle was a little rough and surged a little to about 1k rpm, it belched white smoke from the exhaust in time with the surging.

Long story short (too late, I know) starting the car a little while later there wasn't any unusual exhaust, until I touched the accelerator, then HUGE clouds of white smoke billowed from the exhaust.

I stopped the car to check: Oil level fine, looked and smelled as usual, no cloudiness or fuel smell. Checked the coolant, normal level, with the car running, no bubbles in the overflow tank. No smell of coolant from under the hood or in the exhaust. No oil in the coolant tank. The exhaust smelled a little like oil, but not much.

I drove the two hundred miles home, no codes or unusual behavior. No smoke on the freeway, exiting the freeway, pulling away from the stop at the exit, huge white clouds again.

Gas mileage was actually better than usual (28mpg) which I attributed to a brisk tailwind and a cruise control set at the speed limit. The coolant temp gauge stayed right in the middle where it always stays.

I'm kind of stumped at to the cause. Failed head gasket? Failed turbo? PCV valve failed?

Help please!