Players are unmuted when relog - plugins

Question

I have no idea why my code is not keeping players muted after they relog even though I added them to the config.
This is there the muted players get saved:
private static ArrayList <Player> mutedPlayers = new ArrayList<Player>();
This is the event that handles the muted player and that should check if the player is muted or not:
#EventHandler
public void handlePlayerChat(AsyncPlayerChatEvent e){
Player p = e.getPlayer();
if (mutedPlayers.contains(p)) {
p.sendMessage(ChatColor.DARK_RED + "You've been muted!");
e.setCancelled(true);
}
}
This is the command:
if(command.getName().equals("mute")) {
if (sender instanceof Player) {
Player p = (Player) sender;
if (p.hasPermission("shxr.mute")) {
if (args.length == 1) {
Player target = Bukkit.getPlayer(args[0]);
if (target != null) {
if (!mutedPlayers.contains(target)) {
mutedPlayers.add(target);
p.sendMessage(ChatColor.GREEN + "You have successfully muted " + target.getName() + ChatColor.GREEN + "!");
target.sendMessage(ChatColor.DARK_RED + "You are muted!");
getConfig().set("mutedPlayers.Players", mutedPlayers);
saveConfig();
} else {
mutedPlayers.remove(target);
p.sendMessage(ChatColor.GREEN + target.getName() + ChatColor.GREEN + " has been unmuted!");
target.sendMessage(ChatColor.DARK_RED + "You have been unmuted!");
saveConfig();
}
} else {
p.sendMessage(ChatColor.DARK_RED + "Cannot find the player.");
}
} else {
p.sendMessage(ChatColor.DARK_RED + "Proper usage of this command is: /mute <player>");
}
} else {
p.sendMessage(ChatColor.DARK_RED + "You do not have the permissions to mute players!");
}
}
}

Answer 1

Two issues:
You aren't saving this list to disk, so when the server restarts, you're going to lose it all.
You are storing references to the Player object, which gets recreated any time a user logs in or changes dimensions (Player is just an Entity class and is not a permanent reference). You need to store the user's UUID.