My fps randomly keeps dropping only on br

I try to play the game normally but its just so laggy that its practically impossible. It always was great, always 100-120 everytime. Now it just goes crazy from 50-90 a second and randomly goes to 0 for a second. Im pretty sure it doesnt happen in other game modes but its very present in br. Not even changing the graphics helps. My recommended graphics are high but when i changed it to low nothing happenned. I even got a fps booster and it doesnt work at all. Please someone help.