The new Apple News app, which launched back in September, appears to be off to a pretty good start, but The Wall Street Journal says there’s one big problem: “Neither media companies nor Apple know how many people are reading.”

The app has attracted more than 100 publishing partners worldwide, the article notes, but Apple has reportedly been underestimating the size of its readership and providing that erroneous data to publishers.

The company is said to be in the process of fixing the problem. “Eddy Cue, Apple’s senior vice president of Internet Software and Services, said the company missed the error as it focused on other aspects of the product,” WSJ reports. “The company didn’t explain how the problem occurred or say exactly when it might be rectified.”