Random.Range doesn´t seem to be working (or a switch statement)

Got it working. It seems like switch got called to early or in a to high frequency. I moved it into the OnTick funktion and replaced UnityEngine.Random.Range() with a random functions from System. I didn´t try moving switch without using Unity Random but I´m trying it later. Code is here:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using Random = System.Random;
 using System;
 public class Spawner : MonoBehaviour
 {   public float spawnSpeedCount;
     public float countdownTime = 2;
     public int randomNumber;
     Random rnd = new Random();
     
     // Start is called before the first frame update
     void Start()
     {
         InvokeRepeating("OnTick", 2f, countdownTime);
     }
 
     // Update is called once per frame
     void Update()
     {
          
 
     }
     public void OnTick()
     {
         int randomNumber = rnd.Next(17);
         spawnSpeedCount += 1;
 
     switch(randomNumber)
         {
         case 1:
         Debug.Log(randomNumber);
         randomNumber = 0;
         break;
 
         case 2:
         Debug.Log(randomNumber);
         randomNumber = 0;
         break;
 
         case 3:
         Debug.Log(randomNumber);
         randomNumber = 0;
         break;
 
         case 5:
         Debug.Log(randomNumber);
         randomNumber = 0;
         break;
 
         case 6:
         Debug.Log(randomNumber);
         randomNumber = 0;
         break;
 
         case 7:
         Debug.Log(randomNumber);
         randomNumber = 0;
         break;
 
         case 8:
         Debug.Log(randomNumber);
         randomNumber = 0;
         break;
 
         case 9:
         Debug.Log(randomNumber);
         randomNumber = 0;
         break;
 
         case 10:
         Debug.Log(randomNumber);
         randomNumber = 0;
         break;
 
         case 11:
         Debug.Log(randomNumber);
         randomNumber = 0;
         break;
 
         case 12:
         Debug.Log(randomNumber);
         randomNumber = 0;
         break;
 
         case 13:
         Debug.Log(randomNumber);
         randomNumber = 0;
         break;
 
         case 14:
         Debug.Log(randomNumber);
         randomNumber = 0;
         break;
 
         case 15:
         Debug.Log(randomNumber);
         randomNumber = 0;
         break;
 
         case 16:
         Debug.Log(randomNumber);
         randomNumber = 0;
         break;
 
         
     
         }
         
     }
 }