If you encounter a workstation that has a Realtek NIC that constantly connects to the network and reconnects, I suggest you turn the following settings off or on in device manager:
Auto Disable Gigabit > Relink Battery or AC
Green Ethernet > Disable
Energy Efficient Ethernet > Disable
Thanks to: https://www.sevenforums.com/hardware-devices/304958-realtek-pcie-gbe-family-controller-keeps-disconnecting-my-fix.html for the fix.
PS, this is truly a random fix. This was a shot in the dark right out of far left field and it worked. I was going to replace the NIC as the next step but glad I tried this.