Framerate weirdness

Sometimes when i play i get pretty much perfect performance. Therefore almost no stuttering or fps drops the game flows perfrectly smooth as butter no matter what map or how many players.

But after a few matches, sometimes even on the first match of the day it just feels sluggish and unresponsive. I struggle to aim and everything feels weird. I barely get consistent fps.

I restart the game, and poof problem gone. What is going on ?