The 'popcorn' issue is pretty much linked to one artificial flavor... Diacetyl... anything that involves a buttery taste. Often found in microwave popcorn, hence popcorn lung.

Custards, a popular group of vape flavors, was the main source of it.

The catch?

Diacetyl is also a byproduct of cigarette smoking.

https://www.tandfonline.com/doi/abs/10.3109/10408444.2014.88...

The risk was not considered to be noteworthy among cigarette smokers and food workers who had higher exposure to the chemical diacetyl...

> Further, because smoking has not been shown to be a risk factor for bronchiolitis obliterans, our findings are inconsistent with claims that diacetyl and/or 2,3-pentanedione exposure are risk factors for this disease.

So basically... vaping causes popcorn lung = FUD.

Most manufacturers haven't used Diacetyl in their juice for years (like 7+ years by now).