Rating systems are not zero-sum. The points you lose aren't added to your opponent. Add to that, the site uses Glicko which includes an rating uncertainty value, or Ratings Deviation (RD), which impacts how much a rating changes.
A player with a low RD is considered to have a stable, or accurate rating, and will see lower rating changes after wins and losses. A high RD will give much larger swings.
I went from 2164 to 1785 in 3-check over the course of 7 games, 6 of those were the same opponent. However, when the first game was played, he had a rating of 1746 (after game 1), and when the last game finished he only had 1790!
How is it possible that while i lost ~400 points, he only gained 50?
Where did the 350 other points go? Can any staff answer this?