Collision update speed

Hi there

I hope the titel is not confusing. I didn't know how to phrase my problem. For practicing puposes I'm trying to recreate Temple Run. I'm working right now on the script to "pick up" coins. The way I programmed the game so far is, that the players position is fixed and the ground and the coins are moving towards him. The player has a character controller atached to it and following script:

 function OnTriggerEnter (other : Collider) {
    Destroy(other.gameObject);
 }

The coins have a box collider attached to them, set on trigger.

I have three "rows" where coins can spawn (like in temple run). The script kinda works on the left and right. I can pick up coins. But not all of them. The script "skips" a few. But in the middle it doesn't work at all.

Some ideas why that is?

Thanks, mitti2000