Super annoying. Don't know if it's a Sonos or Spotify issue. Have had tons of connection issues through Spotify connect too ( although this particular issue is happening directly through the Sonos app)
Best answer by UKMedia
I suggest that you power down these devices for 10 secs, allowing each one to complete it's boot sequence before moving to the next:
Any wired network switch
Any wired Sonos device
All other Sonos devices
If possible all other connected devices but I realise this may involve a lot!