Rammus lowering FPS

Played a game against a rammus, every time he entered frame (about 20 minutes into the game) frames would get lowered. I normally am at about 200 fps, pretty constant, never going below 100. For the last 30 minutes of the game I was below 60 fps. My team, who I was in a call with, were having similar problems, with all frames below 60 fps. The other team also had some people in chat say that they had problems. It may not be rammus, but that is our best guess at the problem.