This could be related to Spotify does not play audio, where the PulseAudio client library couldn’t locate the socket under strict confinement.
The X11 access is a fallback path where it will try to read the PULSE_SERVER property on the root window to get the socket path. We merged a fix for this to snapcraft-desktop-helpers to work around this by setting the PULSE_SERVER environment variable here:
You’re not using snapcraft-desktop-helpers, but you could probably incorporate a similar fix in your tizonia-snap-wrapper.sh script.