Why are my frames so low?

Ever since the beginning of chapter 5 Fortnite the game has been essentially unplayable. The game is always stuttering even at the lowest settings. I average about 120-150 fps but whenever I move it always seems to drop down to 30 meaning I can’t do anything of high intensity. I have a i5 9400 and an rtx 4060 TI. Is it time I upgrade my cpu?