I have the guest WiFi enabled on SH3 with a different SSID to the factory setting to match various visitors legacy devices.
Every couple of weeks the guest network stops broadcasting. I log into SH3 and it appears to have reset itself. I get a welcome screen as if its a new install, and the guest network is always switched off with the SSID having reset itself to factory setting?
I've been monitoring things since your last post, and everything was stable until today. The hub appears to have rebooted and reset itself, logged in to the now familiar "welcome to your new hub" and had to re-enable guest network which was switched off.
Unless you can see a cause, I guess we have to go with a replacement SH3 as you suggest.
Try a pinhole reset to factory settings. Push in the pin on the back/side/bottom of the Hub with the end of a paperclip until you feel it at the “stop point” and hold for a "timed" 60 seconds do NOT restart the router after that. Your passwords/passphrase for both Hub and Wifi will revert to those printed on the Hub sticker on its base/side/drawer.
-------------------- Services: HD TV on VIP (+ Sky Sports & Movies & BT sport), x3 V6 boxes (1 wired 2 WiFi,) SH2 in modem mode with Airport Extreme Router. On VIVID200, Talk Anytime Phone, x2 Mobile SIM only iPhones.