Have played a little more with this and noticed a truplay update for my Play:1 speaker which I have done.
Not sure that made any difference.
But what I have noticed is that sometimes for a split second some of my other network devices are listed and then quickly disappear including my Denon AV amplifier and my Google speaker within the device list in the Spotify app.
Weirdly my echo dot is always listed
If I choose to use Bluetooth or AirPlay my Denon AV amplifier is listed along with my Apple TV.
So why does the Spotify app briefly see some of my network devices?
Got to be a glitch with how the app is taking to iOS