Turning down the graphics to low makes no difference. It would if I had long loading times, but for the swing meter, it doesn't appear to make any difference whatsoever (or at least for me).
From what I can tell, there are 2 things that affect the swing meter for me.
1) Friend notifications and invites
2) A sudden and temporary CPU spike with the Chrome window running the game. This doesn't happen all the time and seems to be random. I let the game fully load before starting the swing, but on occassion, CPU usage spikes for no apparent reason after that initial load. The spike in CPU usage is always with the Chrome window running the game.