[GAMEPLAY] Won a game and lost 6 LP??

I am in Plat 5, 0 lp and have recently noticed a red warning sign on my profile and when i hover it, it tells me im being shielded from demotion and if i lose ill be demoted (my mmr is low, so i expected to be demoted anytime now as well.) I played normals in order to practice warwick to tryhard my elo back (since if you want to win these days you sorta have to pick the god champs but anyways i digress). Played a game in full (no dcs etc) and after winning i now have -6 lp? I dont understand