Scripts won't derive from MonoBehaviour

For some time now i've been having an issue with creating C# scripts, where when i make a new script from the unity editor (Create > C# script) and open the script for editing it will not derive from MonoBehaviour.

When i reïmport the script or restart Unity/VS2017 it sometimes fixes the issue, but most of the time i need to delete the script and make a new one until it does correctly add MonoBevahiour.

Manually deleting : MonoBehaviour and re-adding it does change anything either. And there are no errors in the console.

edit: "MonoBehaviour" also doens't highlight in green as it normally would, but instead stays plain white colour

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class Foo : MonoBehaviour // <- does not load correctly
 {
     // Use this for initialization
     void Start() {

     }

     // Update is called once per frame
     void Update(){
 
     }
 }  

Any suggestions as to what more i can try would be very welcome since having to delete/create scripts until it works is quite annoying.

Thanks in advance! ~Remy