Third Party Mirror could not be found in scripts but loaded in project

My environment
Unity 2021.2.11f1
using
Mirror 57.0.0

Like a good boy, i just imported Mirror to my project, create a little network manager and it works,
now i wanted to create an override from a Network Manager and create my own but, just typong "using Mirror" in scripts, there are already errors
so when i check the problem tab in VS Code i got these errors

Code (CSharp):

1. The type or namespace name 'Mirror' could not be found (are you missing a using directive or an assembly reference?) [Assembly-CSharp]
2. The type or namespace name 'NetworkManager' could not be found (are you missing a using directive or an assembly reference?) [Assembly-CSharp]
3.  

what i did was simply

Code (CSharp):

1. using System;
2. using UnityEngine;
3. using UnityEngine.SceneManagement;
4. using Mirror;
5.  
6. /*
7.     Documentation: https://mirror-networking.gitbook.io/docs/components/network-manager
8.     API Reference: https://mirror-networking.com/docs/api/Mirror.NetworkManager.html
9. */
10.  
11. public class MyNetworkManager : NetworkManager

What am i lacking here?

 

Same issue, I notice that Unity removes my reference to Mirror every time it goes back to Unity Editor, which I think is the cause.