Fps drops, what to do

I'm playing Fortnite on a 144hz monitor (always set between 160-200 fps in the game, I play half an hour Fortnite constantly 180 fps +

Then I have drops of up to 80 fps, then it goes again briefly, then there's movement again.

My ping was pretty high today, but fps have nothing to do with the ping?

Ryzen 5 1600Af floor

Rx 480 Msi 8GB

16gb ddr4 2666 Mhz clocked at 3000Mhz, then tested whether it happens at 2666Mhz, YES

What I just notice is that both monitors are scanned, even though only one is on. Maybe it was because of it? = P

SEE photos

Can also just be on your screen, are you wearing Vsync? This makes you can't get more than 144fps and improves the game