YouTuber Markiplier made a big profit on GoPro stock, buying in right before a merger sent the shares soaring — good for him, but the timing raises questions for regulators and other investors.

• Markiplier put up to 30% of his net worth into GoPro when the company looked like it was in serious trouble.
• He crossed the 5% ownership mark in mid-July but took six to seven weeks to file the required disclosure, which is supposed to be made within five business days.
• He then made a GoPro video without mentioning he owned shares, and a merger was announced just days after news of his stake broke.
• The stock more than doubled from where he bought it, turning $9 million into $15 million.
• He says he simply liked the stock, but the size and timing of the bet look suspicious.

Outlook: The late filing and undisclosed stake could draw regulatory attention, and more scrutiny of influencer stock bets is likely.