Just got 9 LP for a win

It was probably a game where Riot issued a loss prevented to the team that lost because maybe they started maintenance or something during that time

When a loss prevention is issued to the losing team, the winning team gets only 50% of the regular LP for winning.

How are you even playing ranked???

Every single person on the other team has a sub 50% win rate all with over 100 games each, lowest was 43% which means their Bronze 3 rating is severely inflated. There's so few people who are that bad theyre the only ones the matchmaking could gather into that game so it's like you just beat a bunch of boosted bronze 5s which doesnt really mean much so it's not worth much