synclist not initialized

Hello, I have a problem that I don’t understand how to solve.
I use unet to run the application over the network. I try to synchronize my list with a “SyncListStruct” type, which is in unet, but when i add my instance using the Add () method, an error occurs:

SyncList not initialized
UnityEngine.Networking.SyncList`1:Add(Cell)


Please explain the reason why this error may appear.

my code:

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

public class WorldClass : NetworkBehaviour
{
    public struct Cell
    {
        public int posX;
        public int posY;

        public int height;
        public bool step;

        public float ownerColorR;
        public float ownerColorG;
        public float ownerColorB;

        public string build;

    }

    public class CellsList : SyncListStruct<Cell> {}

}

code where an error occurs

    public WorldClass.CellsList cellsNet = new WorldClass.CellsList();
    void iniDataWorld() {

        if (isServer)
        {
            if (cellsNet != null && cellsData != null)
            {
               
                for (int x = 0; x < cellsData.GetLength(0); x++)
                {
                    for (int y = 0; y < cellsData.GetLength(1); y++)
                    {
                        WorldClass.Cell cell = new WorldClass.Cell();
                        cell.posX = x;
                        cell.posY = y;
                        cell.height = (int)(10 * Generator.getHeight(KeyGen, x, y, 60));
                        cell.build = "";
                        int numPlayer = Random.Range(0, players.Count);
                        cell.ownerColorR = players[numPlayer].colorVec.x;
                        cell.ownerColorG = players[numPlayer].colorVec.y;
                        cell.ownerColorB = players[numPlayer].colorVec.z;
                       
                        cellsData[x, y] = cell;
                        cellsNet.Add(cell); //Error
                    }
                }
            }
        }
    }

please, explain what I’m doing wrong. Thanks

I solved the problem, I noticed that some client commands stopped running on the server, although previously they worked. I had suspicions that I passed in the command the data type with which unet does not work, although the code editor did not produce any errors. in my case I replaced the transferred data type from Vector2Int to Vector2. After that, all the teams began to work, and along with this, the error "SyncList not initialized"