GetButtonDown is unresponsive

I have been using Catlike Coding tutorial to make a platformer game. After finishing the initial tutorial, I decided to try and give the player a bit more free movement rather than just jumping, but the player character occasionally misses button-presses. Also the player seems to occasionally get stuck and unable to jump, while still able to move left and right.

 using UnityEngine;
 using System.Collections;
 
 public class Runner : MonoBehaviour {
     
     public static float distanceTraveled;
     
     public float maxSpeed;
     public float acceleration;
     public float unacceleration;
     public Vector3 boostVelocity, jumpVelocity;
     public float gameOverY;
     
     private bool touchingPlatform;
     private Vector3 startPosition;
     
     private static int boosts;
     
     void Start (){
         GameEventManager.GameStart += GameStart;
         GameEventManager.GameOver += GameOver;
         startPosition = transform.localPosition;
         gameObject.active = false;
     }
     
     // Update is called once per frame
     void Update () {
     if(Input.GetButtonDown ("Jump")){
         if(touchingPlatform) {
                 rigidbody.AddForce (jumpVelocity, ForceMode.VelocityChange);
                 touchingPlatform = false;
             }
             else if(boosts > 0){
                 rigidbody.AddForce (boostVelocity, ForceMode.VelocityChange);
                 boosts -= 1;
                 GUIManager.SetBoosts (boosts);
             }
         }
         
         if(Input.GetAxis ("Horizontal") == -1){
             MoveLeft ();
         }
         if(Input.GetAxis ("Horizontal") == 1){
             MoveRight ();
         }
         
         distanceTraveled = transform.localPosition.x;
         GUIManager.SetDistance(distanceTraveled);
         
         if(transform.localPosition.y < gameOverY){
             GameEventManager.TriggerGameOver();    
         }
     }
     
     void FixedUpdate() {
 
         if(rigidbody.velocity.magnitude > maxSpeed)
         {
             rigidbody.velocity = rigidbody.velocity.normalized * maxSpeed;
         }
     }
     void MoveLeft(){
         rigidbody.AddForce (unacceleration, 0f, 0f, ForceMode.Acceleration);    
 
     }
     void MoveRight(){
         rigidbody.AddForce (acceleration, 0f, 0f, ForceMode.Acceleration);    
 
     }
     
     void OnCollisionEnter () {
         touchingPlatform = true;    
     }
     
     void OnCollisionExit () {
         touchingPlatform = false;    
     }
     
     private void GameStart () {
         boosts = 0;
         GUIManager.SetBoosts(boosts);
         distanceTraveled = 0f;
         GUIManager.SetDistance(distanceTraveled);
         transform.localPosition = startPosition;
         rigidbody.isKinematic = false;
         gameObject.active = true;
         enabled = true;
     }
     
     private void GameOver (){
         rigidbody.isKinematic = true;
         enabled = false;
     }
     public static void AddBoost(){
         boosts += 1;
         GUIManager.SetBoosts(boosts);
     }
 }