Hi there Ed
I finally founf the problem with my X axis and i really hope this bit of info helps others in the future.
I disassembled the entire X axis and went through every component only to find it was the drive belt! The creality falcon comes with the Xaxis already assembled and I assume the belt had been in a certain position in storage for many months if not years.
Even though the X axis belt was the first thing i tensioned when looking for the error of losing sizes, I never noticed that the small wires or fibres inside the rubber toothed belt were actually broken! So there was a fair amount of actual elastic stretch in the middle of my belt that allowed the drive pulley to go out of pitch in a certain position along its track.
I replaced the belt, re tensioned it, re calibrated the X axis in lightburn and its been holding perfect size for the past few days.
Thank you for your input and I appreciate you going down the rabbit hole with me.
we will be in touch im sure.
kind regards
Clayton