i have a friend who has a top wisdom… she can not engrave over 200 with out it doubling…
I assume you are doing a multi pass burn in the picture otherwise there is no way for it to double. Looks like belts and or toothed pulley is slipping i would look at everything in the y-axis to make sure its tight first, then make sure you are not hitting a limit switch at some point in the burn which would cause the machine to lose position.