“They had yet to see the fruits of their investment, given what the opportunity was, and it was unclear for how long vaping was going to be lightly regulated,” said Scott Dunlap, the chief operating officer at the time. “They were excited and pushing hard.”

Fidelity declined to comment.

The Juul, which looked unlike any other e-cigarette and delivered a far more powerful nicotine punch, was supposed to be the hit product for the company, then named Pax Labs, but a few months in, it appeared to be a bust. Convenience stores and vape shops were not getting their orders because of supply chain problems. Manufacturing defects left some customers with bad batteries, or worse, a condition nicknamed JIM — juice in mouth — with no one at the company quite sure how much of the toxic nicotine substance could be safely ingested.

In a meeting in San Francisco in the fall of 2015, the board of directors decided to remove Mr. Monsees as chief executive, dismiss other senior leaders and effectively take over the company. It would be 10 months before they named another C.E.O.

“I was in that first meeting where you tell the board, ‘We aren’t going to hit the numbers. There are issues; there are problems in the supply chain.’ Not a lot of good news,” said Mr. Dunlap, who said he had advised the company to slow down and take the time needed to fix the problems. He was fired the next day.

The board meeting, which has not been previously reported, was a turning point for the company.

Over the next few years, the company — which became Juul Labs after splitting from Pax in 2017 — would reignite the stale e-cigarette business, grabbing more than 75 percent of the vaping market and tallying more than $1 billion in sales in 2018. At the end of last year, it was valued at $38 billion, more than the Ford Motor Company.

From 2016 to 2018, the years Juul’s growth became astronomical, the number of adult nonsmokers who began using e-cigarettes doubled in the United States, according to an analysis of federal survey data by researchers at the Johns Hopkins Ciccarone Center for the Prevention of Cardiovascular Disease. The study estimates that six million adults were introduced to nicotine via e-cigarettes.