Key fragments not dropping on iOS client

So I've gotten frags previously (I'd say last was 3 weeks ago) but it doesn't seem to be dropping at all anymore. Since the last frag I probably played 100 games, I won 50-60% of them and no frags. I have none in stock either so don't see why am I not getting any. Do I have to get an S to be entitled for a chance of one or what's happening?