Since last week, whenever I try to download things through my browser it starts at the usual speed (up to 18 Mbps) then starts to slow down until it reaches about 500 kbps and stays at that speed. All other sorts of downloads as well as internet speed are fine. I've done a number of experiments: first I tried three different browsers (Chrome, Safari and Firefox) and they all behave the same. Then I tried downloading with my VPN on and off, sill no changes. Speedtest shows nothing wrong. I've also run a full antivirus scan which returned nothing wrong. Any solutions? Could my ISP be limiting download speed? Or is it something else?