Halo 5 ranking system is broken. Win=no rank up, lose=diamond 4 to diamond 2 in two matches. Is 343 fixing this anytime?
Sounds like your CSR is self-correcting to your MMR.
If you want to gain a better understanding of the ranking system feel free to read through Zaedynfel’s matchmaking feedback threads and you can leave your thoughts (provided they are constructive) in the most recent one.