What you are seeing is a result of the environment that the scanner is operating in. Sweep is never guaranteed to operate at a fixed sample rate, this is because it ranges a bit different from traditional LiDAR. We have written a theory of operation that will help you better understand why here: Theory of Opeation.
Try moving the scanner to a different environment and examine the difference in signal strength values. Also, sweep operates best if there is not objects closer than 1m in it's field of view.
Also, I've changed the new user settings to allow for image attachments, sorry about that!