I seem to have had a similar problem after adding the extension kit. Some other changes occurred at the same time, upgrading to Lightburn 1.6. I suspected software was the problem.
It turns how that somehow my offsets were misconfigured. I wound up running the
G10 L2 P1 x0 y0 to reset it to zero and now all is well. I can send the machine off to x410, y750 and it goes. Hit origin (or home) to return and it goes back.