1. Install the All Docks LAN Driver for Realtek for corresponding HP EliteBook model.
2. Reconnect USB-C connection between laptop and monitor.
3. Open CMD in Admin mode and run the command dsregcmd /leave.
4. Put laptop into same status as it was when they tried connecting, laptop off, laptop in sleep mode etc.
5. Follow their same process in getting docked / connected to check if it has fixed the issue.