The Lenovo USB-C Hybrid Dock (40AF) comes with a Realtek chip for the ethernet
connection: r8152 and as far as I can see the displaylink.rules assume, the
correct driver for ethernet were cdc_ncm. 

But no: There is a special r8152 driver, which seems to be included in the
kernel. 

cdc_ncm does not work well with this chip. Suspend leads to crash which causes
strange network effects in LAN.

See this file:
https://build.opensuse.org/projects/X11:XOrg/packages/displaylink-driver/files/99-displaylink.rules?expand=1

Discussion see here:

https://forums.opensuse.org/t/realtek-r8152-build-with-dkms-fails/179813

The displaylink driver is provided by X11:Xorg repo
https://download.opensuse.org/repositories/X11:/XOrg/

Workaround:
- Download r8152 from github, make, sudo depmod -a, sudo make install. Copy the
udev-rules file from downloaded archive to /etc/udev/rules.d. The ethernet
connection will work, until the next kernel update. 

I've no idea why dkms fails with r8152, I've described my efforts in the
openSUSE forum, as linked above. 

I'm a user. It's simply my assumption that the rules file were the culprit.