I have a question about LP gains/losses

So I've been playing for a few years and I have the general understand of the ranking system and how LP works between wins and losses. But just recently today, I was playing some ranked games trying to get to a promotion, I took a break when i had about 78 LP I think. when I came back to continue playing I won another ranked game (giving some sort of positive amount of LP) and I looked to see how close I was now to a promotion series and.... my account has 68 LP?????? I know for certain I had above 70 LP before this game, and it greatly confuses me as to what happened with my account. I looked back at my match history and my previous ranked game and it was also a win, so there is no way I went below my known amount of LP of 70+, this is very strange to me and I would like someone to try and give me their best shot at meaningful feedback.

Can negative LP be granted even in a WIN for poor performance? Is there some sort of small bug that just delays my view of the LP and I never saw my actual amount? (this type of bug sometimes occurs in-game. on scoreboard sometimes cs scores will bug and it'll show a lvl 18 ADC with only 25 minions killed when really its 200+)

Please read this and try to help me,

thanks