After a long time with no particular issues, I changed access point (a router in AP mode to which an Era 100 and Pixel phone both connect) to a newer tri-band model. The speaker remained on 5GHz but the phone is WIFI 6E capable which can offer 2x speed - although it isn’t great at detecting the 6GHz network SSID.
There are two configs - my usual which is separate SSIDs for each band or a more common router setup of a single SSID for multiple bands.
I switched to the 2nd scheme as it’s possible for a device to connect quickly on 5GHz and then switch over to 6GHz. But each time it switched the Sonos mobile app would no longer see the speaker for some reason. These are just WiFi bands - the router and network remain common.
Getting back on to 5GHz with single SSID instantly resolved it until the phone switched to 6GHz again, and having separate SSIDs with the Sonos on one and the phone on the other also works fine - so that’s what I’ve gone back to.
Possibilities include the router, android / the phone, or the app - I’m assuming it’s some subtle combination of factors, but thought it worth mentioning as app to speaker connectivity is the sort of issue that’s posted from time to time.
