Multiple unknown devices connected to my router. Streaming lags.

Started on 8/1/2020 when I was talked out of canceling my service and was lowered to a cheaper 100mbps plan. I can pull good speedtest speeds, however can no longer stream on Disney+ (hardwired xbox) play CoD Mobile , nor load 9gag gifs/videos. Multiple unknown devices appear on xFi app even after many router and wifi password resets. Xfinity has been able to shed NO light on this issue. Odd since similar threads have been submitted for ~4 months.