Constant lag spikes

I’ve been having issues with the internet for awhile now. I would say about a couple of months now. I’ve had about five techs come out here and they still haven’t fixed the issue. I’ve changed the modem, ethernet cable, upgraded the internet, bought a new pc because I thought maybe something in the pc went bad that was causing internet issues but it turns out it wasn’t the pc.

I get constant lag spikes everyday consistently with being directly plugged into the modem/router to my pc. I’ve tried turning the WIFI off to see if any devices are causing interference but I was still getting the lag spikes. I’m not sure what the issue is but I want it fix. I’ve haven’t had issues in the past years, just recently this year I’ve been having a lot of issues. WIFI seems fine while watching videos, doesn’t buffer at all really. Could it be a bad splitter? Or the coax cable from outside bad? Coax cable is underground, I put a request in for them to change it this past Saturday when the tech came out but he didn’t replace it. He also couldn’t come inside to check the connections do to the COVID. When doing speed test it seems to be on point to what I should be getting.