I’m having same trouble.
I have just started using Volumio on RPi 3 (with plug in DAC Raspyplay4) and I can’t tell how thrilled I am with the quality of everything. Everything works amazing from start: fast, stable, excellent sound, etc.
Unfortunately Spotify “disappears” after a while (hours), so stability is not good. It is not clear to me what causes this, but cycling on /off or logging in with same credential on another device may be involved. General Spotify playlist and own playlist buttons are visible, but nothing happens if you click them. Occationally it is possible to view content in either own or generic playlists, but still nothing is playable. On one occation I succeded in getting Spotify back to working condition, by erasing personal settings and typing them back in, but I have started from new image 5 times now, as it appears the only safe way . Playing files from USB works always (and absolutely beautiful too ). Changing Spotify password and disabling/ enabling seems to have no effect. Yes, I have premium and everything is just fine with a fresh image on the SD.