Program: 43924
Project: 43924
Buggy source:
@EventHandler(priority=EventPriority.MONITOR) public void onEntityDamage(EntityDamageEvent EntityDamaged){
  if (EntityDamaged.isCancelled() || (EntityDamaged.getDamage() == 0)) {
    return;
  }
  if (EntityDamaged instanceof EntityDamageByEntityEvent) {
    EntityDamageByEntityEvent e=(EntityDamageByEntityEvent)EntityDamaged;
    Entity dmgr=e.getDamager();
    if (dmgr instanceof Projectile) {
      dmgr=((Projectile)dmgr).getShooter();
    }
    if ((dmgr instanceof Player) && (e.getEntity() instanceof Player)) {
      Player damager=(Player)dmgr;
      Player tagged=(Player)e.getEntity();
      for (      String disallowedWorlds : plugin.settings.getDisallowedWorlds()) {
        if (damager.getWorld().getName().equalsIgnoreCase(disallowedWorlds)) {
          return;
        }
      }
      boolean isInCombatDamager=false;
      if (plugin.hasDataContainer(damager.getName())) {
        PlayerDataContainer container=plugin.getPlayerData(damager.getName());
        isInCombatDamager=!container.hasPVPtagExpired();
      }
      boolean isInCombatTagged=false;
      if (plugin.hasDataContainer(tagged.getName())) {
        PlayerDataContainer container=plugin.getPlayerData(tagged.getName());
        isInCombatTagged=!container.hasPVPtagExpired();
      }
      if (plugin.settings.isSendMessageWhenTagged() && !isInCombatTagged && !isInCombatDamager) {
        damager.sendMessage(ChatColor.RED + "String_Node_Str");
        tagged.sendMessage(ChatColor.RED + "String_Node_Str");
      }
      if (plugin.settings.getCurrentMode() == Settings.SettingsType.NPC) {
        onPlayerDamageByPlayerNPCMode(damager,tagged);
      }
 else       if (plugin.settings.getCurrentMode() == Settings.SettingsType.TIMED) {
        onPlayerDamageByPlayerTimedMode(damager,tagged);
      }
    }
  }
}

Fixed version (ground truth):
@EventHandler(priority=EventPriority.MONITOR) public void onEntityDamage(EntityDamageEvent EntityDamaged){
  if (EntityDamaged.isCancelled() || (EntityDamaged.getDamage() == 0)) {
    return;
  }
  if (EntityDamaged instanceof EntityDamageByEntityEvent) {
    EntityDamageByEntityEvent e=(EntityDamageByEntityEvent)EntityDamaged;
    Entity dmgr=e.getDamager();
    if (dmgr instanceof Projectile) {
      dmgr=((Projectile)dmgr).getShooter();
    }
    if ((dmgr instanceof Player) && (e.getEntity() instanceof Player)) {
      Player damager=(Player)dmgr;
      Player tagged=(Player)e.getEntity();
      for (      String disallowedWorlds : plugin.settings.getDisallowedWorlds()) {
        if (damager.getWorld().getName().equalsIgnoreCase(disallowedWorlds)) {
          return;
        }
      }
      boolean isInCombatDamager=false;
      if (plugin.hasDataContainer(damager.getName())) {
        PlayerDataContainer containerDamager=plugin.getPlayerData(damager.getName());
        isInCombatDamager=!containerDamager.hasPVPtagExpired();
      }
      boolean isInCombatTagged=false;
      if (plugin.hasDataContainer(tagged.getName())) {
        if (plugin.npcm.isNPC(tagged)) {
          isInCombatTagged=true;
        }
 else {
          PlayerDataContainer containerTagged=plugin.getPlayerData(tagged.getName());
          isInCombatTagged=!containerTagged.hasPVPtagExpired();
        }
      }
      if (plugin.settings.isSendMessageWhenTagged() && !isInCombatTagged && !isInCombatDamager) {
        damager.sendMessage(ChatColor.RED + "String_Node_Str");
        tagged.sendMessage(ChatColor.RED + "String_Node_Str");
      }
      if (plugin.settings.getCurrentMode() == Settings.SettingsType.NPC) {
        onPlayerDamageByPlayerNPCMode(damager,tagged);
      }
 else       if (plugin.settings.getCurrentMode() == Settings.SettingsType.TIMED) {
        onPlayerDamageByPlayerTimedMode(damager,tagged);
      }
    }
  }
}