Tested the Intel e1000e driver in Kernel 5.4.1, and this still fails with some Ethernet NICs, but is OK on others..

On my HP Z820, there are two (different) Intel NICs, and the e1000e driver works with one, but fails with the other:

LAN connection to eth0 (Intel 82579LM) fails:
[ 125.292581] userif-2: sent link down event.
[ 125.292584] userif-2: sent link up event.
[ 125.506706] userif-2: sent link down event.
[ 125.506708] userif-2: sent link up event.
[ 125.886810] e1000e: eth0 NIC Link is Up 1000 Mbps Full Duplex, Flow Control: Rx/Tx
[ 126.086928] userif-2: sent link down event.
[ 126.086930] userif-2: sent link up event.
[ 127.087490] userif-2: sent link down event.
[ 127.087492] userif-2: sent link up event.
[ 132.227473] userif-2: sent link down event.
[ 132.227475] userif-2: sent link up event.
…….  ( repeated ) ………………
and ethtool reports:
Speed: Unknown!
Duplex: Unknown! (255)
Link detected: no

But eth1 (Intel 82574L), works correctly:
and ethtool reports:
Speed: 1000Mb/s
Duplex: Full
Link detected: yes

Reverting the e1000e patch mentioned here ( http://rglinuxtech.com/?p=2632 ) fixes the link problem on the failing NIC, as before.

Robert Gadsdon.   November 29th 2019.