As you can see, we won the last game and even so they dredged me from diamond V to diamond IV, I do not understand the ranked system, even when you win or contribute to obtaining the victory, very little progress is obtained, but if you lose because someone abandoned ( I want to assume that he crashed) is punished very hard for losing. I also want to believe that they misplaced an algorithm to make this happen.
If you were evenly matched with the team’s you beat - your only goes up a little bit (I think the minimum in Halo 5 was 15 MMR for Bronze to Diamond, and 3 MMR in Onyx].
But then, if you ‘unexpectedly’ lose to a team ranked well below you… you can suddenly drop a chunk of rank.
Especially if your CSR has drifted higher than your MMR - the system takes the opportunity to pull them back into alignment.
I’m not sure if Infinite works differently to Halo 5. But your CSR shouldn’t drop with a win, even if your MMR and CSR have drifted apart. So it may be different this time around?
The other thing is that they may have a cushioning effect… where your CSR is buffered a bit to stop you losing a rank you have only just earnt.
Could you possibly have just scraped into Diamond V (woo hoo) but then lost a game or two to drop your MMR into Diamond IV territory - but the system buffered your CSR at Diamond V to give you a chance to consolidate it.
Eventually though, it got to the stage where you won a game… but not enough to convince the system you are actually Diamond V… so it finally matched your CSR and MMR back together at Diamond IV.