Program: 33828
Project: 33828
Buggy source:
/** 
 * Event handler for Sign Changes
 * @param e - event
 */
@EventHandler(priority=EventPriority.NORMAL,ignoreCancelled=false) public void onSignWarpCreate(SignChangeEvent e){
  String title=e.getLine(0);
  Player player=e.getPlayer();
  if (player.getWorld().equals(ASkyBlock.getIslandWorld()) || player.getWorld().equals(ASkyBlock.getNetherWorld())) {
    if (e.getBlock().getType().equals(Material.SIGN_POST) || e.getBlock().getType().equals(Material.WALL_SIGN)) {
      if (title.equalsIgnoreCase(plugin.myLocale().warpswelcomeLine)) {
        if (!(VaultHelper.checkPerm(player,Settings.PERMPREFIX + "String_Node_Str"))) {
          Util.sendMessage(player,ChatColor.RED + plugin.myLocale(player.getUniqueId()).warpserrorNoPerm);
          return;
        }
        if (!(ASkyBlockAPI.getInstance().getLongIslandLevel(player.getUniqueId()) > Settings.warpLevelsRestriction)) {
          Util.sendMessage(player,ChatColor.RED + plugin.myLocale(player.getUniqueId()).warpserrorNotEnoughLevel);
          return;
        }
        if (!(plugin.getGrid().playerIsOnIsland(player,false))) {
          Util.sendMessage(player,ChatColor.RED + plugin.myLocale(player.getUniqueId()).warpserrorNoPlace);
          e.setLine(0,ChatColor.RED + plugin.myLocale().warpswelcomeLine);
          return;
        }
        final Location oldSignLoc=getWarp(player.getUniqueId());
        if (oldSignLoc == null) {
          if (addWarp(player.getUniqueId(),e.getBlock().getLocation())) {
            Util.sendMessage(player,ChatColor.GREEN + plugin.myLocale(player.getUniqueId()).warpssuccess);
            e.setLine(0,ChatColor.GREEN + plugin.myLocale().warpswelcomeLine);
            for (int i=1; i < 4; i++) {
              e.setLine(i,ChatColor.translateAlternateColorCodes('&',e.getLine(i)));
            }
          }
 else {
            Util.sendMessage(player,ChatColor.RED + plugin.myLocale(player.getUniqueId()).warpserrorDuplicate);
            e.setLine(0,ChatColor.RED + plugin.myLocale().warpswelcomeLine);
            for (int i=1; i < 4; i++) {
              e.setLine(i,ChatColor.translateAlternateColorCodes('&',e.getLine(i)));
            }
          }
        }
 else {
          Block oldSignBlock=oldSignLoc.getBlock();
          if (oldSignBlock.getType().equals(Material.SIGN_POST) || oldSignBlock.getType().equals(Material.WALL_SIGN)) {
            Sign oldSign=(Sign)oldSignBlock.getState();
            if (oldSign != null) {
              if (oldSign.getLine(0).equalsIgnoreCase(ChatColor.GREEN + plugin.myLocale().warpswelcomeLine)) {
                oldSign.setLine(0,ChatColor.RED + plugin.myLocale().warpswelcomeLine);
                oldSign.update(true,false);
                Util.sendMessage(player,ChatColor.RED + plugin.myLocale(player.getUniqueId()).warpsdeactivate);
                removeWarp(player.getUniqueId());
                Bukkit.getPluginManager().callEvent(new WarpRemoveEvent(plugin,oldSign.getLocation(),player.getUniqueId()));
              }
            }
          }
          if (addWarp(player.getUniqueId(),e.getBlock().getLocation())) {
            Util.sendMessage(player,ChatColor.GREEN + plugin.myLocale(player.getUniqueId()).warpssuccess);
            e.setLine(0,ChatColor.GREEN + plugin.myLocale().warpswelcomeLine);
          }
 else {
            Util.sendMessage(player,ChatColor.RED + plugin.myLocale(player.getUniqueId()).warpserrorDuplicate);
            e.setLine(0,ChatColor.RED + plugin.myLocale().warpswelcomeLine);
          }
        }
      }
    }
  }
}

Fixed version (ground truth):
/** 
 * Event handler for Sign Changes
 * @param e - event
 */
@EventHandler(priority=EventPriority.NORMAL,ignoreCancelled=false) public void onSignWarpCreate(SignChangeEvent e){
  String title=e.getLine(0);
  Player player=e.getPlayer();
  if (player.getWorld().equals(ASkyBlock.getIslandWorld()) || player.getWorld().equals(ASkyBlock.getNetherWorld())) {
    if (e.getBlock().getType().equals(Material.SIGN_POST) || e.getBlock().getType().equals(Material.WALL_SIGN)) {
      if (title.equalsIgnoreCase(plugin.myLocale().warpswelcomeLine)) {
        if (!(VaultHelper.checkPerm(player,Settings.PERMPREFIX + "String_Node_Str"))) {
          Util.sendMessage(player,ChatColor.RED + plugin.myLocale(player.getUniqueId()).warpserrorNoPerm);
          return;
        }
        if (Settings.warpLevelsRestriction > 0 && !(ASkyBlockAPI.getInstance().getLongIslandLevel(player.getUniqueId()) > Settings.warpLevelsRestriction)) {
          Util.sendMessage(player,ChatColor.RED + plugin.myLocale(player.getUniqueId()).warpserrorNotEnoughLevel);
          return;
        }
        if (!(plugin.getGrid().playerIsOnIsland(player,false))) {
          Util.sendMessage(player,ChatColor.RED + plugin.myLocale(player.getUniqueId()).warpserrorNoPlace);
          e.setLine(0,ChatColor.RED + plugin.myLocale().warpswelcomeLine);
          return;
        }
        final Location oldSignLoc=getWarp(player.getUniqueId());
        if (oldSignLoc == null) {
          if (addWarp(player.getUniqueId(),e.getBlock().getLocation())) {
            Util.sendMessage(player,ChatColor.GREEN + plugin.myLocale(player.getUniqueId()).warpssuccess);
            e.setLine(0,ChatColor.GREEN + plugin.myLocale().warpswelcomeLine);
            for (int i=1; i < 4; i++) {
              e.setLine(i,ChatColor.translateAlternateColorCodes('&',e.getLine(i)));
            }
          }
 else {
            Util.sendMessage(player,ChatColor.RED + plugin.myLocale(player.getUniqueId()).warpserrorDuplicate);
            e.setLine(0,ChatColor.RED + plugin.myLocale().warpswelcomeLine);
            for (int i=1; i < 4; i++) {
              e.setLine(i,ChatColor.translateAlternateColorCodes('&',e.getLine(i)));
            }
          }
        }
 else {
          Block oldSignBlock=oldSignLoc.getBlock();
          if (oldSignBlock.getType().equals(Material.SIGN_POST) || oldSignBlock.getType().equals(Material.WALL_SIGN)) {
            Sign oldSign=(Sign)oldSignBlock.getState();
            if (oldSign != null) {
              if (oldSign.getLine(0).equalsIgnoreCase(ChatColor.GREEN + plugin.myLocale().warpswelcomeLine)) {
                oldSign.setLine(0,ChatColor.RED + plugin.myLocale().warpswelcomeLine);
                oldSign.update(true,false);
                Util.sendMessage(player,ChatColor.RED + plugin.myLocale(player.getUniqueId()).warpsdeactivate);
                removeWarp(player.getUniqueId());
                Bukkit.getPluginManager().callEvent(new WarpRemoveEvent(plugin,oldSign.getLocation(),player.getUniqueId()));
              }
            }
          }
          if (addWarp(player.getUniqueId(),e.getBlock().getLocation())) {
            Util.sendMessage(player,ChatColor.GREEN + plugin.myLocale(player.getUniqueId()).warpssuccess);
            e.setLine(0,ChatColor.GREEN + plugin.myLocale().warpswelcomeLine);
          }
 else {
            Util.sendMessage(player,ChatColor.RED + plugin.myLocale(player.getUniqueId()).warpserrorDuplicate);
            e.setLine(0,ChatColor.RED + plugin.myLocale().warpswelcomeLine);
          }
        }
      }
    }
  }
}