In LrC 9.3 Linear Tone Curve, clicking on the curve to create a point results in point jumping upward. Have to drag point into position to anchor point at desired location. Happens to every added point no matter how many points already exist. Always jumps upward. Running on Windows 10.
I've since learned that 1) holding ALT when creating a point solves the jumping problem, 2) holding SHIFT constrains the point to stay on the vertical line while dragging, and 3) holding ALT while dragging allows more precise positioning.