I know a similar bug existed recently and was apparently resolved for normal use cases, but I still have this problem when using Spotify Connect to play to Sonos.  If I don't  use the Spotify app for ~10 minutes, all the notification controls go away (on lock screen and on the notification bar), so there is no easy way to control the music or access the app.  I actually think the app itself closes or goes to sleep, but I'm not certain of that.  The only way to get music control back is to re-open the full app, but this is very slow because it takes a few seconds to re-load the actively playing music.  This bug is very annoying, because music control becomes very slow and cumbersome.  I only have this bug with Spotify Connect/Sonos, and not when listening directly from the app.