Can someone explain how the "next win bonus LP" reward works? I can't seem to find context on it

Do you just get a bonus 20 LP (or varying) on your next win IF you win 2 in a row or something? Does it only work with your main role? Is it not a permanent thing or only for provisional ranks (which I'm pretty sure I'm past)?

Side note.. i made it to plat promos on my main account during preseason fairly easily. And now in silver I keep getting matched with nonstop all lanes losing and hyperfeeders. I was on like a 9 loss streak at silver 2.. Some of these games I can say I can contributed to the loss or didn't carry hard enough, but most of them DEFINITELY are flat out uncarryable.. Is my MMR really high from preseason or something and so it's matching me with insanely low mmr golds?.. even after losing that many matches in a row? lol

Like I keep seeing all golds and plats in my games.. even though im silver 2, and lost a ton..