The only bright spot in Yahoo's business nearly ground to a halt in Q1

Yahoo's so-called Mavens businesses, the engine that CEO Marissa Mayer hopes will revive the company's business, suffered a serious slowdown in revenue growth during the first quarter.

The Mavens, which stands for mobile, video, native, and social, saw revenue increase just 7% year-on-year in the first three months of the year.

That kind of single-digit growth rate would be considered sluggish for any tech business, but it's especially striking given that it's in the supposed growth areas that have been the focal point of Yahoo's turnaround effort.

And it's a serious deceleration from the Maven's previous growth rate. Just one year ago, in the first quarter of 2015, the Mavens revenue increased 58% year-on-year.

Yahoo did not explain what caused the slowdown in the Mavens business.

Sure, the Mavens are now a bigger part of Yahoo's overall revenue, so clocking the same growth will become more difficult. But the Mavens still represent only 33% of Yahoo's total revenue, and slowing down from 58% growth to 7% growth in the span of one year is striking under any circumstances.