Two of Dropbox’s largest mutual fund investors have marked down the value of their holdings in the company by a little over 20% in recent months, the funds disclosed in recent days.

While the reasons for the markdowns aren’t clear, they could reflect the funds’ faltering confidence in the company, valued at $10 billion at its last fundraising early last year. Dropbox’s core business of providing online storage is rapidly being commoditized as Google, Apple and Amazon all offer competing services at lower prices. Dropbox also looks pricey compared to rival Box, which is public and valued at $1.4 billion, despite being expected to generate between half to three-quarters of Dropbox’s estimated revenue this year.