CreateML Preview Tab Miscalculating Sample Duration

I'm training an activity classifier with CreateML and when I add samples to the Preview tab, the length of the sample it displays does not match its actual length.

I have set prediction window size to 15 and sample rate to 10. The activity is roughly 1.5 seconds.

When I put a 1.49 second sample into preview, it says it is 00:00.06 seconds:

and when I put a 12.91 second sample into preview, it says it is 00:00.52 seconds:

Here is the code I am using to print out sensor data in csv format:

if motionManager.isDeviceMotionAvailable {
            motionManager.deviceMotionUpdateInterval = 0.1
            motionManager.startDeviceMotionUpdates(to: .main) { data, error in
                guard let data = data, let startTime = self.startTime else { return }
                let timestamp = Date().timeIntervalSince(startTime)
                
                let xAcc = data.userAcceleration.x
                let yAcc = data.userAcceleration.y
                let zAcc = data.userAcceleration.z
                
                let xRotRate = data.rotationRate.x
                let yRotRate = data.rotationRate.y
                let zRotRate = data.rotationRate.z
                
                let roll = data.attitude.roll
                let pitch = data.attitude.pitch
                let yaw = data.attitude.yaw
                
                let row = "\(timestamp),\(xAcc),\(yAcc),\(zAcc),\(xRotRate),\(yRotRate),\(zRotRate),\(roll),\(pitch),\(yaw)"
                print(row)
            }
}

And here is the data for the 1.49 second sample mentioned above: