Device iPhone 7
(iPhone 8, Samsung Galaxy 9, Macbook Pro late 2016)
(iOS 10, Android Oreo, Windows 10,etc.) iOS 12.3
My Question or Issue
This problem started only recently. Despite being able to control the Sonos volume from the Sonos app slider, I can't use the Spotify slider to control it accurately. It is delayed and then slides back and forth on its own, fluctuating the sound. I can't use the hardware volume control for either Spotify or Sonos. This happens whether I have the Spotify app open only or both the Spotify and Sonos apps.
THIS HAPPENS ONLY WHEN I AM PLAYING SPOTIFY THROUGH SONOS. If playing Spotify alone on my iPhone it works fine, with either the app or hardware volume controls. Same with using only Sonos.
I have the proper settings on for integrating Spotify and Sonos. Also to allow hardware volume control through my phone app. None have been charged from when this all worked. I've used both apps for years. This has never happened before.
I am using an iPhone 7, running iOS 12.3.