Using a pool of objects that will be spawned ONCAMERA and removed OFFCAMERA instead of INSTANTIATE & DESTROY (iOS)

I want to use a pool of prefabs that will be randomly spawned on (random) squares of my board every 4 and collected (and removed from the board) by my character.

The board has 48 tiles, one of which is constantly occupied by my character that moves on it. This leaves 47 tiles available for the spawned tokens to occupy.

My initial approach was instantiating and destroying these prefabs, which resulted in extremely low fps. This way I learned that this practice (frequent instantiating & destroying) is to be avoided in iOS games.

After asking lots of questions and posting here and in the Forum, what Im trying to do now, is use a pool of deactivated prefabs that will be activated when needed, instantly moved to a random tile on board (as If I instantiated them) and deactivated and removed from the board (as If I destroyed them), when my character collects them.

I use the following script, attached to an empty game object:

var popSoundAtSpawn: GameObject; //the sound that plays when a token is spawned var spawnObjects : GameObject[];// this is the Array comprised of tokens that will be randomly spawned var tilesArray : GameObject[];// this is the Array comprised of all squares of the board var tokensPool : GameObject[];//this is the Array comprised of 47 tokens that at maximum will be on board at the same time var spawningRate: float= 3.3; // every spawningRate seconds, one token will be moved on board var delayBeforeSpawningBegins: float =2;// when the level begins, it will wait 2" before it starts spawning tokens var emptySquares: int; var spawnSuccessful: boolean; var tokensSpawned: int=0;

 randomTokenNumber = Random.Range(0,tokensPool.length); // this will choose a random token from the tokens Pool
 var spawnSuccessful = false;
 while (spawnSuccessful == false && (tokensSpawned-characterScript.tokensSwallowed)<47)) {// this makes sure that the tokens spawned minus the ones swallowed by my character are less or equal to my available board tiles, which are 48 (in total) minus 1 that my character occupies = 47. So the while's escape condition, will be met when the board is full of tokens
 var placeToSpawn: GameObject = tilesArray[randomTileNumber]; //the position of one of the randomly selected board tiles. In that position will the token be spawned
 var spawnedToken: GameObject = tokensPool[randomTokenNumber]; // this will pick randomly, one of the tokensPool Array's contents
 if (placeToSpawn.tag == "EmptyTile" && spawnedToken.active == false){  // this checks if the selected tile is empty and if the selected token is one of the deactivated tokens that are still off-board and have not been moved on it.
     iTween.MoveTo(spawnedToken,{"x":placeToSpawn.transform.position.x, "y": 0, "z":placeToSpawn.transform.position.z,"time":0}); //this will move the token instantly, on the randomly selected empty tile's position
     spawnedToken.active = true; //the token will be activated
     tokensSpawned ++; // the number of instantiated tokens will be increased
     Instantiate(popSoundAtSpawn); // the spawning "pop" sound will be played
     spawnSuccessful = true; // the while's escape condition will be met
 }

What happens, is when I hit play, sometimes 5, sometimes 10 (at best) collectibles are activated and spawned in random positions (as expected) and Unity freezes. Am I getting into an infinite loop? Isnt this script a good way to have the token prefbs spawned and removed from the board?

Even if i simplify the "while" line like this:

while (spawnSuccessful == false ) {

I get the same freezing after 5-10 spawns problem. It seems like Unity freezes when it tries to randomly pick a token from the tokensPool, that has already been picked-spawned and is already on the board. I would expect it not to try to pick an already spawned token though, as I use:

spawnedToken.active == false

in the "if" statement.