Just in case this helps anyone else, I found what the issue was. My ISP ended up sending techs out a couple times, and the second guy noticed that the signal strength was actually too strong. He...

@Philbert Thank you for those recommendations. I had my PC set up as one of the priority devices on the QOS, but I have now removed the other 3 devices that were on there so my PC is the only one....

I've been using the Deco M5 mesh network in router mode with 3 nodes since 2018, with very few issues. In the last few months though, I have gotten some staggering lag playing online games, to the...