S3 to b4 in one game good job Riot

Thank you, for the most toxic experience... "one game to decide your new rank" to "fix" a rank bug... If you guys(Riot) would kindly show me in black in white what the algorithm is for MMR and how that decides elo please, because honestly I don't see how i go from s3 to b4 with a loss. That's a bug. However I heard people who were plat one go 10-0 and get b5 so I guys I should be grateful for the b4.... -_-