Senbotsu

Ok, so in a last ditch effort to revert whatever windows broke without just re-installing windows, I ran a TCP optimizer that tweaked a bunch of windows settings and that seems to have fixed it for now.

Ok, having made a boot USB with Kubuntu 19.10 and booted to that, it's definitely windows being a jerk. The speed test was over 900Mbps when ran in kubuntu:

So at this point, either there is something wrong with the adapter that I can't detect with testing equipment (which is possible, I've seen it happen before but it's super rare) or something has gone amiss with windows and it's decided to poop itself. I think my next step at this point is to do a dual boot to either verify or eliminate software as the issue.

11% util: And if I run the same speedtest from a different computer plugged into the same port of the router using the same cable:

Checking the update log, the last system update was on the 30th of last month.. so ~10 days ago. I don't *think* it's the root cause, but I've lost track of how many days I've been trying to fix this issue, lol.

No particularly high resource usage:

If you mean the hardware, quite sure. Especially since I was getting gigabit speeds a few days ago, went to bed, and the next day crap internet. After much hoop-jumping I isolated it to this PC, and I'm assuming at this point that it has to be something windows/software related but short of giving up and doing a clean install (which I don't really want to do) I'm at a loss.

I left it on auto (after forcing it made no change) Edit: never responded to the adapter question, sorry. It's the Intel I219-V integrated adapter that comes with the Asus ROG Maximus Hero XI motherboard.

So this is a bit of a stumper for me. For some reason this PCs connection is being throttled to 100Mbps even though every test I can run says the port is running properly at 1 gigabit, full duplex. Both a LAN data transfer and a WAN speed test choke out around 104-ish Mbps. I've replaced cables, completely removed and done a clean reinstall of drivers, checked bios settings (and updated bios), and tested the adapter itself for mechanical issues. All the other PCs on the network can transfer at 900-1000Mbps both cross-network and internet speed tests. - a Klein port tester reports no problems with the port or SNR issues with the ethernet cables. - adapter status within windows says it's running at 1 Gbps as well: