Anybody notice difference over last month or so on game rank?

I have consistently gotten S- to S on several champs and while I still can, it suddenly got a lot harder. Some champs it seems have become near impossible. When you go 20/4/18 with good cs on jungler and you get A-? I have a few champs I have gotten S on almost every game (Vel Koz // Illaoi // WW) that I get better stats than I have in past and gotten much lower grade. Has there been some change in the last bit on how rankings work? There are a few champs that are a pain in the read to get higher rank (skarner). I can still get S almost every game on Voli. Jungle especially seems harder but support as well. Mid is still easy to S. Are they comparing stats from when devourer and before they buffed camps and jungling was cake? I just feel confused on how I can do better and get worse grades.