For what it's worth, I'm running into this very same issue over 4 years after the original poster. I suspect that leaving off the group option is leaving the process running as group root, which would mimic my attempt at having the service run as user freeswitch/group root, which allows mod_portaudio to function.
I've posted here in the mail list, on IRC and in Slack, but the only bite was someone hinting about freeswitch user needing to be in group audio, which it is. This is broken. I've looked at submitting a JIRA on this, but my login doesn't appear to allow it.