i have the same CPU and had a few problems with temperature turns out my voltage was too high my motherboard is asus z370f.
it set the voltage to something like yours on 4.7ghz, after some help from the guys here. i figured it out and just did an OC on my own managed to get 5ghz on something like 1.25v and i increased that to 1.26v just to be on the safe side.
so i guess motherboard increases voltage to maintain stability i suggest you try to do it your self and not use the default settings since every chip is different, and the z370 bios is not yet mature as far as i know.