base.base.Start is getting called instead of base.Start

It shouldn't miss one if you're calling from the correct subclass.

You'll have to call a virtual method that will be called from the base Start.

i.e.

     public class A : MonoBehaviour
     {
         void Start()
         {
             Init()
         }
     
         virtual void Init() { }
     
     }
     
     public class B : A
     {
         override void Init()
         {
             base.Init();
         }
     }

     public class C : B
     {
         override void Init()
         {
             base.Init();
         }
     }
 

Or make Start a virtual method that's overridden and you call base too

 public class A : MonoBehaviour
 {
     protected virtual void Start()
     {
 
     }
 }
 
 public class B : A
 {
     protected override void Start()
     {
         base.Start();
     }
 }

 public class C : B
 {
     override void Start()
     {
         base.Start();
     }
 }