Weird bug. Roll a ball project

I'v been working on the roll-a-ball project from the learn section. I recently added a "Speed" text field and I noticed that when I first start playing, if press W or S then the speed will not go above 3.8 (or below -3.8). If I go left or right just a hair, this will fix the problem and I can move with W and S as normal. The same fix happens if I bump the ball into a wall. The glitch also does not occur if I start the ball out at (.1, .5, 0) in the editor instead of (0, .5, 0). Just incase I somehow screwed the code up I'll paste it below.

 using UnityEngine;
 using UnityEngine.UI;
 using System.Collections;
 
 public class PlayerController : MonoBehaviour {
     public float moveSpeed;
     public float accelSpeed;
     private int pickupCount;
     public Text countText;
     public Text winText;
     public Text speedGage;
 
     void Start(){
         pickupCount = 0;
         setCountText();
         winText.text = "";
         speedGage.text = "0";
     }
     void FixedUpdate(){
         updateMovement();
 
     }
     void updateMovement(){
         float moveHorizontal = Input.GetAxis("Horizontal");
         float moveVertical = Input.GetAxis("Vertical");
         Vector3 movement = new Vector3(moveHorizontal,0,moveVertical);
         rigidbody.AddForce(movement * moveSpeed * Time.deltaTime);
         speedGage.text = rigidbody.velocity.ToString();
     }
     void OnTriggerEnter(Collider other){
         if(other.gameObject.tag == "PickUp"){
             other.gameObject.SetActive(false);
             pickupCount += 1;
             setCountText();
         }
     }
     void setCountText(){
         countText.text = "Count: " + pickupCount.ToString();
         if(pickupCount == 16){
             winText.text = "You Win!";
         }
     }
 }