Internet randomly capped to sub 100mbps

I have an internet plan thats supposed to give me 150mbps, which it used to give without any issues. However recently its just been capped below 100mbps, often getting stuck at specifically 86mbps or 94mbps. I used wifi on my phone to check and its giving me 150mbps as its supposed to but my pc for some reason does not. I did get an entirely new system but I don't exactly know what or where the issue could be. I tried connecting my phone's internet to my computer via tethering and that seemed to work fine, giving me speeds well over 300mbps.