Animating position but it moves in Y dimension only

Godot Version

4.3

Question

I have a platform (AnimatableBody2D, Sprite2d and collisionshape2D) which I am trying to animate using AnimationPlayer.

In the Godot editor, I can see the platform moving around nicely, exactly as I want.

But when I play the game, it moves in the Y dimension only! It just moves up and down at wierd speeds. Its not animating the X at all.

Running the game should really do exactly what the editor just showed me. Any ideas?