Not sure if this is GeneratePress related 100%, but on my speedtests (even with blank page/test page) I am having the favicon.ico file load very late. I noticed this also happening on the speedtest.generatepress site for me in GT Metrix/Pingdom.
I.e. site itself loads in ~200-300ms, nothing happens for some time, then favicon.ico loads. For tools like GT Metrix, it then says the total load time.. which seems a bit unfair.