Earlier today, Valve released a small patch which saw the addition of stats for Neutral items. A welcome quality of life chance, but then players started reporting a weird bug - they automatically gained or lost thousands of MMR points.
As a result, multiple pro players like Saksa have breached the 10,000 MMR mark.
From what we can tell, players who finished the match when Dota 2 coordinator was offline or right after the patch was released, are the ones who are primarily affected by this issue. If their last game ended with a victory, they gained thousands of MMR. If they lost, they lost the same amount.
Many have theorized that this is due to the server trying to process matchmaking data, over and over again but ultimately failing. Each time an iteration was run, MMR was distributed.
Valve has not commented on the bug. The MMR shifts that have occurred due to this bug will likely be reversed by the game when they fix this issue.