Have you tried raising & lowering it to the highest/lowest points the WorkFit-D can go? You can reset it this way -- Raise it up to its heighest level, and then while it's lowered down at it's lowest point, push on the top of the desk - you should hear a "click" type noise. Afterwards, try raising and lowering it - and locking it. This should resolve your issue.
Let us know your results!
All the best,