Diagnosis
Slowed, struggling movement usually points to voltage issues or the motors being under excessive load, often from the desk being out of level or the frame binding.
How to Fix It
First, check the simple stuff. Make sure the desk is plugged directly into a wall outlet, not a power strip or surge protector. Those can limit current. Next, clear everything off the desktop. Lower it all the way, then raise it empty. Listen for straining noises and feel if one side lags. If it moves smoothly empty, your load is likely okay. The problem might be that the desk's minimum height was accidentally set too high. Do a full memory reset (hold down arrow 10 sec, long beep, then hold down again to descend fully). This clears any incorrect limits making the motors work against themselves.
If That Didn't Work
If it's still slow and weak even empty, check that the floor is level. Put a small level on the desktop. If it's off, the frame is twisted, causing constant resistance. Loosen (don't remove) the bolts connecting the desktop to the side frames, let the desk settle on the floor, then re-tighten. This can re-distribute the strain.
Heads Up
The Core model has a published weight capacity. Exceeding it with heavy monitor arms, PCs, or stacks of books will permanently slow the motors and lead to early failure. Distribute weight evenly and keep it under the limit.