iOS downloads rose by 7.3 percent in May, increasing to an average of 4.54 million apps a day in the U.S., reports user acquisition company Fiksu.

According to the company’s latest App Store Competitive Index, the volume of daily app downloads for the top 200 free apps in the U.S. has begun to recover after falling for three straight months, the fallout from Apple’s crackdown on download bots. Although not acknowledged by the development community, artificial downloads were a tactic used by some developers to propel their apps to the top of the charts in order to attract real customers. While download volume has rebounded this month, app downloads are still down more than 33 percent from January’s all-time high of 6.79 million apps a day in the U.S.

While app download volume recovered in May, the cost to acquire a loyal user — defined as someone who opens an app at least three times — dropped 13.7 percent to $1.26, falling to its lowest point since February.

Fiksu credited the decline in user acquisition costs to uncertainty regarding the upcoming phase-out of Unique Device Identifiers (UDIDs). Apple will soon prevent apps and services from using the 40 digit long alphanumeric codes to track users, and the lack of a clear alternatives has cooled advertising spend, says Fiksu CEO Micah Adler.