Quite some time ago i went on a bad losing streak playing while tilted and tanked my 1v1 MMR down to near 4000. I made a comeback more recently and was like halfway back to 5000, having played like 300 games. The other day I played a few games, a couple of which didn’t get promptly recorded. Then i played a few more and suddenly my MMR shot up nearly 400 points, and at the same time, my record had also been reset, as it showed me as having a 4-0 record instead of the hunrdeds of games I’d played. So apparently what happened was everything except my MMR somehow got reset, and I gained large amounts of points because the system treated them like placements (or something).
At first I thought they started a new season early or something. But it turns out that only my Human 1v1 record was reset, everything else is unaffected.