Program: 34091
Project: 34091
Buggy source:
/** 
 * Prevents teleporting when falling based on setting
 * @param e
 */
@EventHandler(priority=EventPriority.LOW,ignoreCancelled=true) public void onPlayerTeleport(final PlayerTeleportEvent e){
  if (debug) {
    plugin.getLogger().info(e.getEventName());
  }
  if (!e.getFrom().getWorld().getName().equalsIgnoreCase(Settings.worldName)) {
    return;
  }
  if (!Settings.allowTeleportWhenFalling && e.getPlayer().getGameMode().equals(GameMode.SURVIVAL) && !e.getPlayer().isOp()) {
    if (plugin.isFalling(e.getPlayer().getUniqueId())) {
      e.getPlayer().sendMessage(Locale.islandcannotTeleport);
      e.setCancelled(true);
      if (e.getPlayer().getLocation().getBlockY() < 0) {
        e.getPlayer().setHealth(0D);
        plugin.unsetFalling(e.getPlayer().getUniqueId());
      }
      return;
    }
  }
  Island islandTo=plugin.getGrid().getProtectedIslandAt(e.getTo());
  Island islandFrom=plugin.getGrid().getProtectedIslandAt(e.getFrom());
  if (islandTo != null && islandTo.getOwner() != null) {
    if (islandTo != islandFrom) {
      if (islandTo.isLocked()) {
        e.getPlayer().sendMessage(ChatColor.RED + Locale.lockIslandLocked);
        if (!plugin.locationIsOnIsland(e.getPlayer(),e.getTo()) && !e.getPlayer().isOp() && !VaultHelper.checkPerm(e.getPlayer(),Settings.PERMPREFIX + "String_Node_Str")) {
          e.setCancelled(true);
          return;
        }
      }
      e.getPlayer().sendMessage(Locale.lockNowEntering.replace("String_Node_Str",plugin.getPlayers().getName(islandTo.getOwner())));
    }
  }
}

Fixed version (ground truth):
/** 
 * Prevents teleporting when falling based on setting
 * @param e
 */
@EventHandler(priority=EventPriority.LOW,ignoreCancelled=true) public void onPlayerTeleport(final PlayerTeleportEvent e){
  if (debug) {
    plugin.getLogger().info(e.getEventName());
  }
  if (!e.getFrom().getWorld().getName().equalsIgnoreCase(Settings.worldName)) {
    return;
  }
  if (plugin.getGrid() == null) {
    return;
  }
  if (!Settings.allowTeleportWhenFalling && e.getPlayer().getGameMode().equals(GameMode.SURVIVAL) && !e.getPlayer().isOp()) {
    if (plugin.isFalling(e.getPlayer().getUniqueId())) {
      e.getPlayer().sendMessage(Locale.islandcannotTeleport);
      e.setCancelled(true);
      if (e.getPlayer().getLocation().getBlockY() < 0) {
        e.getPlayer().setHealth(0D);
        plugin.unsetFalling(e.getPlayer().getUniqueId());
      }
      return;
    }
  }
  Island islandTo=plugin.getGrid().getProtectedIslandAt(e.getTo());
  Island islandFrom=plugin.getGrid().getProtectedIslandAt(e.getFrom());
  if (islandTo != null && islandTo.getOwner() != null) {
    if (islandTo != islandFrom) {
      if (islandTo.isLocked()) {
        e.getPlayer().sendMessage(ChatColor.RED + Locale.lockIslandLocked);
        if (!plugin.locationIsOnIsland(e.getPlayer(),e.getTo()) && !e.getPlayer().isOp() && !VaultHelper.checkPerm(e.getPlayer(),Settings.PERMPREFIX + "String_Node_Str")) {
          e.setCancelled(true);
          return;
        }
      }
      e.getPlayer().sendMessage(Locale.lockNowEntering.replace("String_Node_Str",plugin.getPlayers().getName(islandTo.getOwner())));
    }
  }
}