If one or more of your devices is actively using data it can sap bandwidth (speed) from something else you are trying to do. Many connected devices can use data without you knowing it. Satellite TV receivers, Smart devices, Chromecast background images, devices saving info to and retrieving info from the cloud, device updates, Windows 10 sharing updates to others on the net (Delivery Optimization), a weak WiFi connection, etc.
This page can show you what is connected, and what was, but is no longer.
I'm sure a rep will reply regarding the radio issue.
Hope this helps.