Some buyers of Apple's new MacBook Pros are finding that the three-finger drag gesture is working inconsistently on their trackpads, if at all, according to complaints on Apple's support forums and elsewhere.
Where the problem is intermittent, it may manifest only on some parts of the trackpad. Some owners, including people on MacRumors forums, have speculated that the issue is related to palm rejection technology.
Either way it's unclear if the issue is a hardware or software defect, and Apple hasn't officially acknowledged the situation. Both 13- and 15-inch systems are being impacted.
Three-finger drag is available with OS X Yosemite or later, and can be used to reposition windows without moving the mouse cursor and clicking. It can be toggled through OS X/macOS's trackpad settings, located under the Accessibility section of System Preferences.