unity relative movement goes up or slow

hi everybody, i have a small problem dealing with movement control, when i put my camera like a third person, it works well, but when put the camera above or on a iso side to the player, the player start to have probleme (goes through the ground or away, or being slow on Yaxis)

my camera just follow my player transform.position and here is my code for the player :

void Movement() { float moveHorizontal = Input.GetAxis("Horizontal"); float moveVertical = Input.GetAxis("Vertical");

 Vector3 movement = new Vector3(moveHorizontal, 0.0f, moveVertical);
 movement = Camera.main.transform.TransformDirection(movement);

 transform.Translate(movement * speed * Time.deltaTime, Space.World);
 if (movement != Vector3.zero)
     transform.rotation = Quaternion.Slerp(transform.rotation, Quaternion.LookRotation(movement.normalized), 0.2f);

}