Only Getting Key Fragments From Games

So I've had this problem for quite some time now and I never really put much thought into it until I realized I had a total of 15 key fragments from all the games I played over the past month. Ever since about a month ago, I've kept receiving key fragments whenever a teammate or I got an S- or above and/or a win in game on a regular 5v5 matchup. In that one month, I haven't even received 1 Chest... yet I somehow got 15 key fragments. Could it be possible that the ratio is this lopsided and I'm just getting unlucky for not getting chests, or is this an actual bug?