Why won't music play in the background? – Shades: A Simple Puzzle Game Review

I've been playing this game for years, it's my go to on air travel. However, Spotify will no longer play in the background. It doesn't happen with any other app but this one. This is not how it was before. I don’t play as often now because I can’t listen to music in the background.
Review by Annek2016 on Shades: A Simple Puzzle Game.