I just bought a new computer with a i7-7700k, ryzen 580, 16gb ram, 650w power supply, and a Z270 MSI motherboard. I have installed fortnite and counter strike and I average above 144 on both easily. After installing Rainbow Six Siege I get on average 100 fps but it spikes every 3-4 seconds down to 30-40 fps. In the settings it says that it is using my graphics card but I don't know why the fps constantly spikes.
I downloaded HWINFO and am linking two screenshots, before and after sorry I don't really know what I'm looking at hope that it helps. I tried downloading MSI Afterburner but it gave me an error when I try to run it saying because of it's side by side configuration, not sure what that means. The product and serial number of my motherboard from CMD is Z270 GAMING PLUS (MS-7A75) & I316133341.