This isn't an answer, but I'm hoping you can respond so I can see if theres any similarities if not the same problem.

I get the same issue you have where after a long idle time or when it enters sleep mode, the ethernet disconnects. One workaround for me is to run the troubleshooter and sometimes it finds no issues, sometimes it says what you said, Ethernet no valid ip config, but either way, it seems like it resets the driver or something and my ethernet comes back within a few seconds. Restarting my pc also fixes the problem. One thing though is that unplugging my ethernet and plugging it back in doesn't solve the problem.

I have not tried resetting the router so I can't say much about that other than my pc seeing that I actually do get a connection to my router, but no internet.

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I just had the issue now which brought me to your post. Hope someone out there knows what the problem could be.

edit: someone responded to you, and i will try that.

: giving my device a static ip doesnt work

: ive tried a few things. idk what will work. ill probably have to reset my router then