I never said it has nothing to do with the MMR. I’ve explained the exact opposite. What you’re doing is assuming it has nothing to do with the MMR, and instead blame it on a non-existent bug.
But I’ll do you a solid and explain your picure too, which you linked to above:
As explained already, when it says “your matchmaking value” it refers to your team’s matchmaking value. As in the average MMR of you and the other 2 in your party at the time, which is when it ended in that picture.
Meanwhile, why you didn’t gain any rating with 4 rounds won, was because you gained little per win when you did win, and lost a lot when you lost, due to the MMRs of those rounds.
Blizzard even explains it clearly themselves: