Quick update from me. I’ve had the issue again even in the same network. When I open Spotify and play a song it plays on the phone. I can then select an echo device to play it on but the volume doesn’t work. A simple quick fix was to send the sound back to the iPhone and then back to the echo and bingo! The 2nd time I connect to the echo device I can control the volume immediately. Strange ! Bit it works for me.