The ball being an static body is odd... I suspect the
Area2D is not detecting the static body at all, see the issue: Area2D does not detect moving StaticBody2D.
I would like to encourage to change the ball to be either a
KinematicBody2D in Godot 3.x) or a
RigidBody2D. Your code should be easier to adapt to
KinematicBody2D as you can continue to move it by the same means.
RigidBody2D might save you the code for the ball bouncing (you might want to remove gravity), but you need trickery to teleport it...
Note: If you are using Godot 3, you would use
Physics2DServer instead of
Consider also using areas around the playing field, either using big
WorldBoundaryShape2D (which is intended for this use case).
For advice on which physics body to use consider: When should I use a KinematicBody or a RigidBody for 2D platformer characters?