Bad pcv?

I have a 2015 b8.5 S4 with 104k miles. About 4 weeks ago I got a low coolant warning. When I popped the hood, the coolant was almost entirely gone, after it was full the day before. My mechanic says it was an air bubble and to just fill it up which I did. I filled it up to almost full and now it is at the minimum line so it is slowly leaking coolant with no visible leak.

There is white smoke, very little, but besides that the car is running perfectly.

Is this a bad pcv?