Ball not rolling fast on first movement

Hi, I recently completed the Roll-a-ball tutorial, and have been trying to fix some issues with the movement of the ball. On the first time I try and move the ball either vertically or horizontally, it does not roll to its maximum speed. To get it to its maximum speed, I have to roll it on the other axis as well. For example, if I started rolling the ball downwards, I would have to roll it sideways to get it to start reaching its maximum speed. Also, rolling the ball diagonally makes it work again.

Another issue is diagonal movement- I tried to normalize the vector so that the ball doesn't move faster diagonally, but it rolls at a vector of 0.7,0,0.7 for example, while when it rolls down its vector is 1.0,0,0. Is this correct behaviour or should I multiply the vector by the 'magic number'? This is my code for the movement of the ball:

 void FixedUpdate()
         {
             Vector3 direction = new Vector3 (Input.GetAxis ("Horizontal"), 0, Input.GetAxis ("Vertical"));
     
             if (direction.magnitude > 1) 
             {
             direction.Normalize ();
             }
             rigidbody.AddForce (direction*speed*Time.deltaTime);
             print (direction);
         }