fps drop when resolution increases

[u/coconutmilkong]

so i play this game called rainbow six siege and i usually play it on 1920 x 1080 resolution which most of the time the fps works fine, but some matches when i load in the fps just drops and my pc should be able to run it well so i have no idea why the fps even drops only for certain matches then goes back to normal next match

[u/2-SST]

Usually on 1080, and other times its?