Just throwing it out there the ranking system is still broken. You can only rank down, if you win a game you get almost no CSR.
The latest Matchmaking Feedback topic explains in detail what is going on right now
https://www.halowaypoint.com/en-us/forums/58b8518e005f432381ab99fbcaf931e0/topics/matchmaking-feedback-update-%e2%80%93-may-21/7d3f6e81-5f9e-44f7-b5cf-30f85d13f320/posts