Latitude 5290 drops Internet when in hibernate

One of our users has a 5290 that drops the internet connection when it is in hibernate/sleep mode. When it wakes, the only thing that will get the internet back is rebooting the machine. When the device drops the internet connection is random, as client has come back to see no email updates for hours, so I'm sure it does not happen when client is trying to wake from hibernate. I have searched the forums here, but the responses only refer to WiFi being dropped. This machine uses the WD15 dock to connect via ethernet to a network and, conversely, does not appear to drop the internet connection when on WiFi. We have updated the dock and ran all updates through Dell Command Manager on the machine. I have looked at the ethernet card in Device Manager, but it does not have tabs that indicate it uses power saving (as I saw on another post). I have made sure the card is running the latest drivers. The machine is connected to 2x Dell P2317H monitors that have had power saving turned off. Would like to know if anyone has any suggestions as we don't know where else to look.