Solved Malfunctioning code

I use this code to block not useful commands and players can't login. What's wrong?

Code:

    List<String> whitelist = Arrays.asList(new String[] {
            "/ereply", "/er", "/l", "/login", "/msg", "/m", "/emsg", "/tell", "/etell", "/t", "/whisper", "/ewhisper", "/w", "/informacje", "/regulamin", "/spawn", "/r", "/reply", "/register", "/reg", "/logout", "/changepassword", "/changepass"
            });
  
    @Override
    public void onEnable(){
        Bukkit.getServer().getPluginManager().registerEvents(this, this);
    }
  
    @EventHandler
    public void onPlayerCommandPreprocessEvent(PlayerCommandPreprocessEvent e){
     if(!whitelist.contains(e.getMessage().toLowerCase())){
         if(!e.getPlayer().isOp()){
             e.setCancelled(true);
             e.getPlayer().sendMessage("§f§lUnknown command.");
         }
      }
    }

Also that happens:
- I'm opped, I leave server
- I join server and i can't login

 

@Urag Is your server offline mode? That would be the issue

 

@bwfcwalshy I switched to online mode and happens the same.

 

@timtower How to check it? Seems that servers takes OP until not logged.

 

@timtower AuthMe is the problem :<

 

I know the issue, it's a very simple logic issue but not helping due to offline mode. Kinda surprised this hasn't been locked already honestly. Either way, good luck, you should support Mojang though and use online mode.