Diagnosis
The two lift columns are out of synchronization. One motor is receiving power late or has more mechanical resistance.
How to Fix It
Perform a full recalibration. Lower the desk completely until it stops. Press and hold the 'Down' button for 5 seconds until the long beep. The desk will rise to max height, which resets the synchronization. Test the movement. This fixes 90% of tilt issues.
If That Didn't Work
One of the lift column assemblies is likely failing. Listen closely to each leg during movement. A struggling motor will sound strained. The faulty column needs replacement.
Heads Up
Never try to manually force or push the desk to level it during movement. You can damage the gearbox. Let the calibration routine run its course.