public class GroundChecker : MonoBehaviour {

    private Character player;
    private void Start()
    {
        player = GetComponentInParent<Character>();
    }
     private void OnTriggerEnter2D(Collider2D collision)
       {
           if ( collision.gameObject.layer==8)//8 слой-слой с объектами по которым можно ходить
           {
               player.onGround = true;
              
           }
    
    }
    private void OnTriggerStay2D(Collider2D collision)
    {
        if (collision.gameObject.layer == 8)
        {
            player.onGround = true;
        }
    }
//Проблемный участок//
    private void OnTriggerExit2D(Collider2D collision)
       {
           if (collision.gameObject.layer==8)
           {
               player.onGround = false;
      
           }
       }
    

}

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class MonsterBehaviour : MonoBehaviour {

    public float speed = 3f;

    public Transform[] waypoints;
    private int ArrayIndex;

    void Start () {
  ArrayIndex = 0;
    }
    

    void Update () {
  

  transform.position = Vector2.MoveTowards (transform.position, waypoints[ArrayIndex].transform.position, speed * Time.deltaTime);
  CheckWayPoint ();
    }

    void CheckWayPoint(){
  int test = ArrayIndex + 1;

   if (Vector2.Distance(transform.position,waypoints[ArrayIndex].transform.position)<0.1f) {
   if (test > 1) {
    ArrayIndex = 0;
   } else {
    ArrayIndex++;
   }

    }
}
}