Steps to reproduce

1) Create an empty HDRP project

2) Create SG Lit and a material instance off of it

3) Click on Add Precomputed Velocity {+}first{+}, it will auto enable Motion Vectors for Vertex Animation

4) Open frame debugger, search for MotionVectors

5) Observe only CameraMotionVectors pass exists

6) Click on Motion Vectors for Vertex Animation first and then enable Add Precomputed Velocity

7) Check frame debugger, observe ObjectsMotionVectors pass exists