MMR bug in duos

Hello im playing a lot of duos in battlegrounds. Im around 7500 mmr and gain around 70-90 mmr for a win. Twice now I’ve come up with the bug that when there are three teams left and you knock one of the teams out and the other team leave themselves the mmr gain is low. in both instances ive tried this I gained around 13-20 mmr for a first place in duos.