We have a number of Latitude E5450's which all have the most up to date drivers installed and are all fully patched up running Windows 7. However the issue only arises when the laptop is docked and is left for say 30 mins to 1 hour. Once woken up the 'domain name' associated with the LAN (wired) adapter shows as unidentified network.
The fix seems to be to right click the adapter and diagnose. Once done is comes back saying 'doesn't have valid IP configuration' and that it is fixed.