Ranging error quantization is credible?

Hi all,
I’ve setup a test bench to make statistical analysis on the measurements.
I put a pair of Tags at fixed distance of 70 cm on top of a wooden table.
I put an anchor on the wall in front of me at about 430 cm
I connected a PC to collect the two results while moving forwaard and backward the pair of Tags synchronously.
The movement was made in steps of 1 cm every ten seconds and using a squared peace of paper to control the movement alignement.
Hope to be clear in describing the setup.
The results are very strange.
As you can see in the attached picture, while moving from 427 cm to 450 cm the measurements show the expected noise (hi frequency) but do not exhibit something similar to a progressive increase of the measure. It appears, sometime, changing in opposite direction (decrease while increasing the distance) and jumps suddenly by about 5 or 10 cm like if the error was affected by some quantization. Ex See blue line between 800 and 2000 and the pink line between 1500 and 2500.
Is this due to the clock frequency? is it something like the wheels spinning in reverse direction when viewed in a movie?
Any idea? Of course it is a bad condition when making Kalman filtering or etecting direction of movement.
Thanks for any suggestion on possible misinterpretationon my side.