problem with object pooling in infinite runner

hello guys!
i recently created a infinite runner 2d in unity with 2 different environment that each has 4 parent Game object included sky, ground, trees and... so i make a list and add instantiated these parent Game objects for random using. the problem is: when last random number equals to current random number that takes game object from the list are same , parent game object that is player on it and is using, reposition to next position and under feet of player get empty and player falls!

using System.Collections;

using System.Collections.Generic;

using UnityEngine;



using System.Linq;



public class LevelGeneration : MonoBehaviour

{

    public GameObject[] world1;

    public GameObject[] world2;

    List<GameObject> world1List;

    List<GameObject> world1ListB;

    List<GameObject> world2List;

    List<GameObject> world2ListB;

    public GameObject player;

   

   

    // float[] width1;

    // float[] width2;

    // Transform[] startPos1, startPos2;

    // Transform[] endPos1, endPos2;

   

   

    private Vector2 screenBounds;

    public Camera mainCamera;

    public int iterateCount = 10;

   

    Vector3 nextPos=new Vector3 (-5,0,0);

    float Width;

    Vector3 currentPos;

    Collider2D groundCollider;

    Collider2D playerCollider;

    Transform[] startPos1, endPos2, startPos2, endPos1;

    Queue<GameObject> queueList;



    public Transform rePositionPoint;



    public Transform generationPoint;

    Time timer;

   

    // Start is called before the first frame update

    void Start()

    {

        world1List = new List<GameObject>();

        world2List = new List<GameObject>();



        world1ListB = new List<GameObject>();

        world2ListB = new List<GameObject>();



        queueList = new Queue<GameObject>();



        currentPos = transform.position;

        //width1 = new float[world1.Length];

        //width2 = new float[world2.Length];

        startPos1 = new Transform[world1.Length];

        endPos1 = new Transform[world1.Length];

        startPos2 = new Transform[world2.Length];

        endPos2 = new Transform[world2.Length];

        playerCollider = player.GetComponent<Collider2D>();



        screenBounds = mainCamera.ScreenToWorldPoint(new Vector3(Screen.width, Screen.height, mainCamera.transform.position.z));

   

        for (int i = 0; i < world1.Length; i++)

        {

            GameObject c1 = Instantiate(world1[i]) as GameObject;

            Width = c1.GetComponent<BoxCollider2D>().bounds.size.x; //all width same

            groundCollider = c1.GetComponent<Collider2D>();

            startPos1[i] = c1.transform.Find("startPos");

            endPos1[i] = c1.transform.Find("endOfSet");

            //width1[i] = c1.GetComponent<BoxCollider2D>().bounds.size.x;

            c1.SetActive(false);

            world1List.Add(c1);

        }

        for (int i = 0; i < world1.Length; i++)

        {

            GameObject c2 = Instantiate(world1[i]) as GameObject;

            Width = c2.GetComponent<BoxCollider2D>().bounds.size.x; //all width same

            groundCollider = c2.GetComponent<Collider2D>();

            //startPos1[i] = c1.transform.Find("startPos");

            //endPos1[i] = c1.transform.Find("endOfSet");

            //width1[i] = c1.GetComponent<BoxCollider2D>().bounds.size.x;

            c2.SetActive(false);

            world1ListB.Add(c2);

        }



        for (int i = 0; i < world2.Length; i++)

        {

            GameObject c1 = Instantiate(world2[i]) as GameObject;

            Width = c1.GetComponent<BoxCollider2D>().bounds.size.x; //all width same

            groundCollider = c1.GetComponent<Collider2D>();

            startPos2[i] = c1.transform.Find("startPos");

            endPos2[i] = c1.transform.Find("endOfSet");

            //width1[i] = c1.GetComponent<BoxCollider2D>().bounds.size.x;

            c1.SetActive(false);

            world2List.Add(c1);

        }

   

       

       

       

    }



    // Update is called once per frame

    void FixedUpdate()

    {

       

       

       

        if(player.transform.position.x + screenBounds.x > currentPos.x + Width/2)

        {

            GameObject c ;

            int rand1 = Random.Range(0, world1List.Count);

            c = GetPooledObject(world1List)

            c.transform.position = nextPos;

            c.SetActive(true);

            world1List

            nextPos.x += Width;

            currentPos.x = c.transform.position.x;



           

        }

       



       

    }



    GameObject GetPooledObject(List<GameObject> list)

    {

        int rand = Random.Range(0, list.Count);

        if(!list[rand].activeInHierarchy)

        {

            return list[rand];

        }

        GameObject c = list[rand];

        return c;

       

    }

   



   

}