[IN GAME] WIN WORTH 9 LP / LOSE 0 LP BUG

Okay so i just played a game with Lux Mid. We were losing from 20 kill or so and i've been able to carry back to our win. This isn't my issue, the problem is that i only won 9 LP when i usually win 23-28LP. And when i talked about this in the game chat, all my team had 9 LP and the other team didnt lose any LP. I don't report this ''error'' so the other team lose LP which idgaf. I just want to understand if it was an MMR error or LoL error. And if its a LoL can i have the 12-15 LP back.

( i really don't think its an MMR error since we were all 10 to have an error due to LP )

Don't mind to hit me igm or back on this topic if you don't understand something, i know i don't have a perfect english.