Ethernet connection turns off when my Mac idles

I had similar problem with the wifi I use.

It would disconnect me after certain time of inactivity.

So when downloading big stuff it would disconnect me, unless I was active on the computer/web.

To prevent wifi been disconnected during long downloads or me not interacting with it:

In Terminal I entered following:

ping -i600 google.com

That would send a ping to Google than wait 600 seconds to send another ping and on and on...till I hit the control-C to stop it.

That will tell wifi I am active so it will stay up all the time.

The 600 sec (10 minutes) is a choice, and it worked for me. In my case it was the WiFi service provider that cut me off after been inactive for a while.

I think it may be because the location may be set to automatic. I would try the method here: https://wccftech.com/fix-internet-not-working-after-waking-mac/ - Use the method titled "Fix Internet Not Working Issue After Waking Your Mac Up From Sleep" - Just thought I would share if those are still looking for options to try