Animation does not work

Hello! I have a problem that I have been dealing with for a long time, it happens that I have a code to animate the items in an inventory, that is to say that the item in the inventory will change when prompted
Example:
SLOT 1: IRON_SWORD
wait 3 seconds ...
SLOT 1: DIAMOND_SWORD
As my code works "well", it is capable of animating the items but a problem occurs, it happens that I have Material.valueOf (itemList.get (itemIndex));
and I also have an if to know when the itemIndex has already toured the entire ArrayList of materials
if (itemIndex <itemList.size () - 1) {
i ++;
} else {
i = 0;
}
This goes through the list again.
The list is as follows:
https://pastebin.com/bLcq8xfE
In this list you can see that the size of the lists are not equal, there are 2 lists whose size is 1 and the last list is of size 0. Then it happens that the itemIndex returns to 0 because it has already crossed the list that has size 0, then the animation does not occur because it does not go through the other lists.
I will leave my code for greater understanding .
Code:

Code:

package me.LobbyBrain.Inventory;

import java.io.File;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.UUID;

import org.bukkit.Bukkit;
import org.bukkit.ChatColor;
import org.bukkit.Material;
import org.bukkit.configuration.file.FileConfiguration;
import org.bukkit.configuration.file.YamlConfiguration;
import org.bukkit.entity.Player;
import org.bukkit.event.inventory.InventoryCloseEvent;
import org.bukkit.inventory.Inventory;
import org.bukkit.inventory.ItemStack;
import org.bukkit.inventory.meta.ItemMeta;
import org.bukkit.scheduler.BukkitRunnable;
import org.bukkit.scheduler.BukkitScheduler;
import org.bukkit.scheduler.BukkitTask;

import me.LobbyBrain.Main;

public class Inv{
 
    private Main plugin;
    public Inv(Main plugin) {
        this.plugin = plugin;
    }
 
    InventoryVersionHandler ivh = new InventoryVersionHandler();
    public static HashMap<UUID, Integer> taskMap = new HashMap<UUID, Integer>();
    public void inventoryContents(Player player, String fileName) {
        File file = new File(plugin.folder(), fileName);
        FileConfiguration config = YamlConfiguration.loadConfiguration(file);
        Inventory inv = Bukkit.createInventory(null, 54, "");
        BukkitScheduler sc = Bukkit.getServer().getScheduler();
        sc.scheduleSyncRepeatingTask(plugin, new Runnable() {
            List<String> items;
            List<String> displayname;
            int itemIndex = 0;
            int    displayNameIndex = 0;
            int X;
            int Y;
            ItemStack stack;
            ItemMeta meta;
            @Override
            public void run() {
                for(String itemkey : config.getConfigurationSection("Inventory.Items").getKeys(false)) {
                    items = new ArrayList<String>(config.getStringList("Inventory.Items."+itemkey+".ID"));
                    displayname = config.getStringList("Inventory.Items."+itemkey+".DisplayName");
                    //meta = stack.getItemMeta();
                    X = config.getInt("Inventory.Items."+itemkey+".X");
                    Y = config.getInt("Inventory.Items."+itemkey+".Y");
                    if(config.getConfigurationSection("Inventory.Items."+itemkey).contains("Lore")) {
                        List<String> listlore = config.getStringList("Inventory.Items."+itemkey+".Lore");
                        List<String> list2 = new ArrayList<String>();
                        for(int i = 0;i < listlore.size();i++) {
                            list2.add(listlore.get(i).replace("&", "§"));
                            meta.setLore(list2);
                        }
                    }
                        stack.setItemMeta(meta);
                        stack = new ItemStack(Material.valueOf(ChatColor.translateAlternateColorCodes('&', items.get(itemIndex))));
                        inv.setItem(Y*9-1-9+X, stack);
                        player.sendMessage(""+items.get(itemIndex));
                        if(itemIndex < items.size()-1) {
                            itemIndex++;
                        }else {
                            itemIndex = 0;
                        }
                }
             
            }
         
        }, 0, 20);
        player.openInventory(inv);
        //taskID(player, fileName);
    }
    public int taskID(Player player, String fileName) {
            int task = Bukkit.getServer().getScheduler().scheduleSyncRepeatingTask(plugin, new Runnable() {
            File file = new File(plugin.folder(), fileName);
            FileConfiguration config = YamlConfiguration.loadConfiguration(file);
            List<String> titleName = config.getStringList("Inventory.Title");
            int i;
            @Override
            public void run() {
                        if(i < titleName.size()-1) {
                            i++;
                        }else {
                            i = 0;
                        }
                        ivh.versionHandler(player, titleName.get(i));
            }
        },0, 20);
         
            taskMap.put(player.getUniqueId(), task);
            return task;
    }
}