Speaker Connections not showing suddenly

[charic]

I've a fairly well connected smart home and suddenly a bunch of devices aren't showing in the spotify connect list

1 x sonos play 1
5 x Google nest audio (2 pairs and a single)
1 x chromecast

Spotify apps are up to date, speaker firmware is up to date, router is up to date.  All have been power cycled but things are still not showing in the connect list and it's driving me a bit mad.

I can get around it by speaking to the nest speakers which seems to establish a connection but I'd prefer to be able to interact without speaking.

Router is a BT Smart Hub

Any thoughts on the culprit?  Is it the spotify app and I'm a bit doomed?  Or is the router a bit rubbish and needs swapping out?