I see no name of the ISP, no make/model of anything so all I can offer is the shot in the dark. I'm going to be wrong but turn off WiFi in the usual supplied modem.
So for about a week my Internet has been causing me problems. I have a 30 mbps internet from my provider and for the past week ill get on my games and after about an hour or so my speeds will drop down to as low as .27 mbps and last most of the day..the ping is fine on the speed tests its just the speed.
i contacted my isp and they came out and looked at everything (of course it was workin fine when they were here) and they checked the lines and said everything was fine. The next day its acting up again so i go get a new modem and hook it up and still problems....call the isp again and they said theres no problems on their end. i dont know what it could be
i have it connected directly from the modem to my desktop