Power down all Sonos, reboot the router, close the Controller.

Power up Sonos and re-open the controller, with any luck you’ll have all back.

You can likely avoid this by setting static/reserved IP addresses for your Sonos using your router’s DHCP settings page. It is usually just a few clicks, not rocket science.

Neither the Sub nor the Play:3 support Bluetooth.

I am guessing that message is from your OS (Android?) as a pre-requisite to enabling WiFi.

If problems persist, post a screenshot of this Bluetooth message.