Created attachment 180002 [details]
Screenshot showing all tools and their readings.

SUMMARY
System Monitor reporting incorrect network speed for Some hardware while other tools are reporting it correctly (atop and bmon).

STEPS TO REPRODUCE
1.  (I am willing to help debug on my machine if you can provide instructions) or Get an AQUANTIA AQC107 chip LAN Controller, 10G/5G/2.5G/1G/100Mbps RJ45 NIC Card ( I got it off aliexpress for around 50CAD.
2.  Start the download of a large file (or any network activity such as speed measurement)
3.  Open system monitor and look at history plot for network.

OBSERVED RESULT
Speed keeps going up and down and reaches double the actual value. For instance if speed is 13MiB/s you will see 26MiB/s on and off pattern. The integral under the curve might be correct but I am sure it is not real because using other tools I am reading correct values consistently. Also If I do a speed test I reach double the true maximum of the network adapter on one computer and the real speed on another adapter on the other computer for the same test.

EXPECTED RESULT
I expect to see a smooth realistic plot of the true network speed as reported by other tools atop and bmon for instance See picture for comparison. (note that 

SOFTWARE/OS VERSIONS
Operating System: NixOS 25.05 (Exact version below and here you can get the ISO https://releases.nixos.org/nixos/unstable/nixos-25.05beta772522.1e5b653dff12)
KDE Plasma Version: 6.3.3
KDE Frameworks Version: 6.12.0
Qt Version: 6.8.2
Kernel Version: 6.13.7 (64-bit)
Graphics Platform: Wayland
Processors: 24 × 12th Gen Intel® Core™ i9-12900K

ADDITIONAL INFORMATION
    "nixpkgs": {
      "locked": {
        "lastModified": 1742669843,
        "narHash": "sha256-G5n+FOXLXcRx+3hCJ6Rt6ZQyF1zqQ0DL0sWAMn2Nk0w=",
        "owner": "nixos",
        "repo": "nixpkgs",
        "rev": "1e5b653dff12029333a6546c11e108ede13052eb",
        "type": "github"
   }
}