Have you tried disconnecting the cable between your Mac and the dock for 10 secs then reconnecting?To add the product MAC Address to the "Mar" table is that something only the internet operator can do? or can i do it by myself?
Looks like you're not the only one who's had issues. Some of the comments on the linked page say it works if you disconnect/reconnect the USB-C connection. Apparently a bug with the Realtek chipset not working after waking from sleep. Looks like you'll have issues every time the system sleeps.
Ethernet port is not working
If you're experiencing the Ethernet port is not working. Please refer one of the following things below: 1.) Make sure the cable connection setup is correctly. Rear USB-C port is for the USBC pow...hypershop.zendesk.com
Hi, I reply to this post because my ethernet adapter (brand "Uni" but with Realtek RTL 8153 inside) was working out of the box but was however not working after sleep. I always had to unplug / replug it on my MacBook Pro M1 to make it work.
I finally bought the "official" Belkin adapter from Apple web store and now it works after sleep. I checked in the system logs and, as said by different sources, the chipset inside this Belkin adapter is exactly the same as my previous one: Realtek RTL 8153.
So, beware, all RTL 8153 adapters do not seem to be working the same with Mac M1 / Big Sur!