This is a known issue with the macOS provided Ethernet driver for the Realtek Ethernet chipset in several of our Thunderbolt 3 docks and many other docks, Ethernet adapters, etc on the market currently. We’re working with Realtek to get an updated driver to provide to our customers as soon as possible, though at this time we do not have an exact estimate when the driver development will be finished.
For now, we recommend to disable sleep and it should prevent these issues from occurring, or leave sleep enabled and use WiFi temporarily (and disconnect the Etherent cable).
Best wishes,
Josh