Volume control via iPhone button

I know this has been a topic since a while here. But this unsolved issue- I can only agree with many others in this forum - is extremely disturbing! In the past I was still able to change volume via hard button of my iPhone - but since some month also after restarting the phone (which used to work before) this is not working anymore. For volume change always need to open Spotify and then press the volume button to find the slider on the screen (or open the Node App) - very uncomfortable for the probably most basic function!! 🙁