Y travel correct for 23 of 25 inches, then last 2 inches, Y is inaccurate

I have a K2 KG3925, around a 2009 unit. Servo machine driven by Gecko drivers with ballscrews on all 3 axis. It has cut thousands of parts without an issue.

Recently the parts have been "off" in the Y only. And only parts that are well away from the "Y Zero" position. The machine has 25 inches of Y travel and cuts perfectly for the first 23 inches or so. Then, somehow the Y axis goes out of scale and loses accuracy at the furthest reach from the home position.

I installed a new servo motor with new encoder, same result. All the mechanics seem fine, the ballscrew is free, no backlash, no issues, bearings have no slop, both radially and axially.. Pulleys, belts and setscrews checked.

I don't know much about the Gecko drives. Could one be going bad and cause this? Anyone run into this issue?