I have five Nest cameras, two second generation (1 battery and 1 floodlight) and three wired older (Approx. two years old).
After several weeks/sometimes months of working fine, my three wired cameras disconnect and my second generation cameras keep on working. Distance wise, the two working second generation cameras are working are located the farthest away which leads me to think its not a distance issue. I bought a new Nest Wifi (AC2200) hoping to correct the problem, and once again the wired cameras disconnected after several weeks. To get them back on line I have had to delete and reinstall the wired cameras.
Thanks for posting here in the Community and for sharing with us what you've done. Let's see what we can do here. To confirm, are you getting any error messages? Are there devices or appliances (such as baby monitors, microwaves, cordless phones, etc.) near the camera? What is the light status of your Nest Camera while it's disconnected?
Give these steps a try in case the issue happens again:
Keep us posted.