White smoke on startup (AOS replaced last year)
 

Could the AOS have failed again? Or is there another potential cause, it rarely smokes but it really drops a bomb when it does.

Always possible, try removing the oil fill cap while the engine is idling; if it is very hard to get off, the AOS is on its way out.

I've had a similar experience. Not "dropping a bomb" but two or three times on start up it's generated oil smoke for a few seconds. I've no idea why, but I've read that it's not uncommon. I'd still like to understand it and prevent it if possible.

When the smoke event happen had you started the car at sometime and just run it briefly then shut it off? I have had it occur a couple of times when I start it and just move on the driveway. The next time that I start it up, I get a puff of smoke. If I run it for a few minutes and then stop it I have no issues.