List().Add freezes Unity

I have a method that I try call and it just freezes when it reaches the biggestTiles.Add (list [x, y]);. I've tried eliminating every single line, and I'm pretty sure that's the cause of the freeze. It doesn't seem to have a problem with adding it to a completely new List of GameObjects inside the loops, but the biggestTiles List just doesn't seem to like that specific GameObject, or something. The tiles are not null or destroyed. And I can't even debug the error since Unity hangs before anything can be printed. Commenting those lines makes the game run fine, but without the intended functionality.

 public void ChooseWeakPoint(GameObject[,] list){
         //Loop trough tiles to check for highest elapsedToBuff
         var biggestTiles = new List<GameObject>();
         float biggestValue = 0f;
         for (int x = 0; x < 5; x++) {
             for (int y = 0; y < 3; y++) {
                 var comp = list [x, y].GetComponent<BattleButton> ();
                 if(comp.buffCoroutine == null && comp.elapsedToBuff > biggestValue && comp.ButtonState != ButtonStates.Disabled && comp.ButtonState != ButtonStates.Occupied ){
                     biggestValue = comp.elapsedToBuff;
                     biggestTiles.Clear();
                     //biggestTiles = new List<GameObject>(); // Tryed using instead of Clear(). Still doesn't work.
 
                     //var newList = new List<GameObject> (); // Creating a new list inside the loop seems to work
                     //newList.Add (list [x, y]);             // It added the GameObject with no problem.
                     //biggestTiles.AddRange (newList);       // But when trying to add it to biggestTiles, it freezes Unity.
 
                     biggestTiles.Add (list [x, y]);          // THIS FREEZES UNITY
                 } else if (comp.elapsedToBuff == biggestValue) {
                     biggestTiles.Add (list [x, y]);          // THIS ALSO FREEZES UNITY
                 }
             }
         }
         //Choose a tile from the selected biggestTiles
         if(biggestTiles.Count > 0){
             int rand = Random.Range (0, biggestTiles.Count);
             GameObject chosenTile = biggestTiles [rand];
             chosenTile.GetComponent<BattleButton> ().elapsedToBuff = -999;
             chosenTile.GetComponent<BattleButton> ().FadeTileForBuff (3f,ElementTypes.WeakPointBuff);
         }
     }