So, my MMR is shite for what rank I am (S3 MMR for S2). I won two games for a total LP of 36, first game 19LP and second game 17LP. Then I lost because of discord in my team. After three games, I have a total of 15LP. Can someone tell me how you lose 21LP from a single game?
the game believes that your MMR is lower than what you are playing in (basically you belong either where you're at or a rank below).
Therefore it is making you lose MORE LP per loss than per win because it is trying to keep you in your current MMR.
After a while of you winning 2/3rds of your games the system will revise your MMR and reduce your losses. thus causing you to climb ranks again (at least until you get forced into promos where you need a 60% WR to promote)
TLDR - you're stuck because the riot mmr system thinks you belong where you are. play more games while maintaining above a 50% WR average and you'll start climbing again
