DIAGNOSIS: The legs are out of sync. This is a common issue with dual-motor desks if they lose calibration or one leg encounters more resistance.
FIX: You need to re-sync the legs. 1) Lower the desk all the way down. Keep holding the down button for 2 seconds after it stops to ensure it's at the true mechanical bottom. 2) Now, press the up button to raise it about 6 inches and stop. 3) Press and hold the "M" button and the "down" button together for 5+ seconds until it beeps. This tells the controller to re-learn the starting point for both legs. 4) Raise it to full height. It should now move up and down evenly.
IF THAT DIDN'T WORK: One motor might be struggling due to an uneven floor. Check that all four feet are firmly on the ground. If one foot is spinning in the air, adjust it by turning the foot clockwise to lower it until all feet have weight on them. Then repeat the sync procedure from a truly level starting position.
HEADS UP: A small, temporary desync (like a half-inch difference) during normal use isn't a crisis—the controller will often correct it over the next cycle. But if it's several inches off and getting worse, do the sync fix immediately to avoid straining the frame.