LP gain malfunction?

Ok, so i've been working hard on the soloQ grind, and it's been going great. I was getting 23-27 per win and really doing work, then all of the sudden, i started getting only 18 per win.... but considering i have a +20 win record i feel like this shouldnt be happening? Plus, it was incredibly spontaneous?

The only reasoning i have is that i duo'd one game with a friend and we lost (he's same elo), and since then i've been devastated by the lack of LP gains....

Help?

I'll try to get a screenshot up to prove my case