Raspberry Pi 3 and HifiBerry Digi+ running Volumio 2.246.
After configuring playback options to hifiberry digi, I could play my spotify tracks and using web radio. No volume control worked.
Then I set volume control to software and I was able to adjust volume for web radios, but sound from spotify was gone.
I then returned to None as mixer option but still spotify has no sound at all.