This is a good article.

The ingredient is diacetyl (DA). It is the aroma in butter flavored popcorn.

It does not mean you have to stop eating butter flavored popcorn. Moderation is good and more important is limiting the inhaled vapors from the bag of microwave popcorn.

There are some butter flavorings that have diacetyl (DA) in them. I could not find them by looking at ingredients because they list "artificial flavorings" rather than the specific artificial flavoring.

I read a report about this issue some time ago when a factory that used diacetyl (DA) had wide spread health problems with their production line workers. They identified diacetyl (DA) and also listed some sprinkle on flavoring that use the same substance. The biggest problem was the inhalation factor. Inhaling it can overwhelm the blood brain barrier.