apple tv v3 drops wifi connection

I own two instances of an Apple TV v3. Everything worked perfectly well for two-three years. Then, on the first, and then later the second, the Apple TV would come on and run for a while (minutes, or tens of minutes) and then drop the connection. The report is "your apple tv isn't connected to the internet". And checking the settings, the WIFI connection has disappeared. I have tried "restarting" and also "cold booting" the Apple TV. (And the modem as well.) All to no avail.

Has anyone developed an answer to this problem? Or has Apple simply designed their Apple TV to fail? Do we know? (There are many, many, others who report this problem on the web.)

Thanks,
Mike