[LocalPCGuy]

Sounds like you found the issue but for future reference or for anyone stumbling across this later on, another thing to check is network ports in the "cheap" (i.e. generally most < $100) USB/USB-C hubs/port expanders with a power passthrough and a network port.

I had a pretty bizarre experience where it would work just fine during the day while the computer was on, but when I'd shut the lid of my work MacBook, the network port on that little USB-C hub would just start sending off ACK signals like crazy, killing my network for anything else trying to use it (effectively denial of service myself). It was really hard to track down also because it wasn't "traffic" really, and it didn't happen on the devices that were impacted (i.e. I'd be using my Windows PC in the evening and that was attached to my work computer). Even more perplexing because it was semi-random - turned out it wasn't "random", it was when I shut the lid of my work laptop vs. just leaving it up and walking away. I finally saw the flood of traffic by dumping network traffic and was able to trace it back to that hub (first I thought my laptop was pwned and was doing something like exfiltrating data or mining when I wasn't logged in, but it was very definitely the hub after a bit more digging).

Since discovering that, I have come across others that have written up the same or similar issues. With the power passthrough, the hub still has power, and if the network interface is flaky as many are, it can cause issues, particularly when the machine it's plugged into stops using it.

This post has links to a few various write-ups: https://mjtsai.com/blog/2022/05/11/usb-c-hubs-breaking-ether...