How to spawn 2 events with a score gap..?

I've want to run two spawning events after a gap of 50 in score..till 50 first event spawn after that next event start and first one stops..But it works only till the score of 200..not after that..Can you find the problem or give a easy approach how to achieve this ?

    void FixedUpdate()
 {
     
         if (player.spawnCon == 1) 
         {
             if ((player.score - prevScore) > 50) 
             {
                 prevScore = player.score;
                 temp++;
                 if (temp == 1) 
                 {
                     c = 1;
                 }
                 else if (temp == 2)
                 {
                     c = 2;
                     temp = 0;
                 }
         
             }
              }

             if ((horizontal == 1) && ((c == 1) && (a == 0))) 
             {       //JUMPING
                 a = 1;
                 b = 0;
                 Invoke ("Spawn", Random.Range (2, 5));
             }
         
             if ((c == 2) && (b == 0))
             {//DOWNWARDS
                 b = 1;
                 a = 0;
                 Invoke ("Spawn", Random.Range (2, 5));
             }
         
         }
     }
     
 }


 void Spawn()
 {
     if (player.spawnCon == 1 && isCloud == 0) 
     {
         if ((horizontal == 0) && ((player.score < 50) || (c==2))) 
         {          //DOWNWARDS
             Instantiate (obj [Random.Range (0, obj.GetLength (0))], transform.position, Quaternion.identity);
             Invoke ("Spawn", Random.Range (spawnMin, spawnMax));
         } 
         else if ((horizontal == 1) && (c == 1)) 
         {              //LEFT TO RIGHT
             Instantiate (obj [Random.Range (0, obj.GetLength (0))], transform.position, Quaternion.identity);
             Invoke ("Spawn", Random.Range (spawnMin, spawnMax));    
         } 

     }
     
     
 }