My ISP is 400/20 package and I have asus ac1900 and wire to deco m4 as AP. I wire from 1 node of deco to my desktop coz my pc is far away from the modem and asus router and I want wire. I do speedtest and it shows 450 mbps down and 21mbps up. However, when I tried to download a file from youtube, the download speed hit 55 mb/s for a few second then it drops to 30 mb/s. Is it because of the ISP or the youtube server or my router or the deco m4? Thank you.