Snapchat has been marked down by one of its principal investors in the third-quarter, fueling an ongoing debate over the accuracy of private company valuations.

According to The Financial Times, Fidelity wrote down the value of Snapchat’s stake by 25 percent to $22.91 in September, based on data from the investment research firm Morningstar. At the end of June, Fidelity had valued each share at $30.72.

While the company, known for its disappearing message service, recently announced that its users watch 6 billion videos a day through its app, the Financial Times reports that the company does not appear to have convinced marketers that its advertising formats will yield a profit.

“There’s huge potential but as yet there isn’t a proposition that is clearly identifiable. I think they are not yet in the stage really of defining how they can make brands live on the platform,” Nigel Morris, chief executive of Americas, Europe, Middle-East and Africa at Dentsu Aegis Network, the advertising agency, told the Financial Times.

The markdown comes as a number of mutual funds struggle to put a price tag on private companies. A recent article in The Wall Street Journal, for example, noted a large discrepancy in valuing Uber, the world’s most highly valued startup. As of June 30, mutual-fund managers at BlackRock Inc. valued the firm’s stake in Uber at $40.02 a share, while Hartford Financial Services Group Inc. said $35.67, and Fidelity Investments said $33.32, the newspaper reported.

Katie Reichart, director of mutual fund research at Morningstar, said that there is no standard for how private companies are valued, making it difficult to discern the true value of a company.

“I think it’s just tough to have consistency in pricing until there’s an IPO,” Reichart told the Los Angeles Business Journal.