Plan

Free (as I'm trying to solve this issue first)

Country

UK

Device

Google Pixel 3

Operating System

Android 10

My Question or Issue

Hi
I'm new to Spotify, as I'm looking for a replacement to Google Play Music which will end this year some time.
I have on my network 3 Sonos speakers. I can cast to any of them perfectly fine through the Sonos app on my Android phone (Pixel 3), and perfectly fine through the Google Play Music App. However when using Spotify, the Sonos speakers do not appear on the list of "Devices Available" 100% of the time. Sometimes I'll get them all listed, other times just one. Most of the time, none of them are listed as available.
When they do show up on the list, I can play to them just fine. Does anyone know why they aren’t showing up consistently?
When they don’t show up on the list, I can immediately go into the Google Play Music app and connect to them through that first time, every time.

I have tried rebooting my router, resetting my Sonos speakers, moving my Sonos from a wireless to wired setup, but none of these made any long lasting effect.

Thanks