Xfinity Router/Modem Combo SEVERE loss in range

Recently, my router only extends about 20 feet in connection range, where as before, all devices in the home could connect from any room. I can stand by the router, connect, walk up the stairs (max 20 feet) and the connection will be lost. As soon as I go back down the stairs, I can connect again. The internet is working, and when I am connected I have no issues. Any guesses for why this happened so randomly? I didn’t change anything to the location/wiring/package.