Unstable Internet

Hi,

I am having an instability problem for a week, mostly not a problem but interfering with gaming a lot. Unfortunately, Xfinity test only tests for speed, so it says it is great, but the test results from other websites show that the speed varies a lot and creates random lags. (average ping: 40ms, sometimes ping goes to 300ms or further)

In this regard, I tried unplugging the co-ax cable, restarting the router, and clearing all the spaces between the router and the computer, which is connected via wi-fi. Nothing helped.

The issue only started recently, so I wonder how to fix it. The AI assistant does not help at all, and I really need real human's help.