Having kind of similar issues with Intel I219-LM (rev 0x00) on two
machines, not sure if related but perhaps worth mentioning. Also
replaced cables and tested different ports. Both machines have issues
negotiating speed, but only if the cable is disconnected and
reconnected. It tends to show up as 10baseT. If the cable is connected
at boot time or after a suspend/resume it always negotiates 1000baseT.
Forcing manually 1000baseT also works.

Additionally one of them drops the link repeatedly under heavier
network load, above 40MB/s and after a few seconds comes back OK, then
in a minute drops again. Tested the same setup with FreeBSD, no issues
there.

On Wed, Apr 2, 2025 at 5:09 PM Stuart Henderson <stu@spacehopper.org> wrote:
>
> On 2025/04/02 13:03, Stuart Henderson wrote:
> > So, have swapped the cable and switchport, let's see what happens next.
>
> ...and that didn't help.
>