I know this is a reply to an old thread, but I
hope this note will be useful. On an Apu2
connected to a cable modem with a gigabit
port, I was also getting only 100baseT.
After reading the replies to this 2018 post,
I checked the cables and found that while
the cables were cat8, they were also
being run through an old APC Back-UPS
for surge protection. Once I connected
the PcEngines Apu2 directly to the cable
modem, I could resume bathing in the
glorious light of 1000baseT.
A hearty thank you to all who replied
regarding checking the cables!