Users have reported a behavior on Dell systems with the Intel I218-LM ethernet adaptor. The ethernet will lose connection when resuming from sleep or hibernation. The system will need to be rebooted or the user will need to disable / enable the ethernet adaptor to get the connection back.
Users have corrected this behavior by disabling the "Allow the computer to turn off this device to save power" option in Device Manager (Figure 1).
Figure 1
Should the behavior remain, users can update to the latest ethernet driver from Intel: Network Adapter Driver