Howard Nurse, W6HN
I suspect the Mumble server (Murmur) may not be starting up. In RigPi Help there are several troubleshooting steps to try in Technical>Troubleshooting>Can't connect to Mumble server.
One "gottcha" on Raspberry Pi's is a setting in /etc/mumble-server.ini. Look for "Specific IP or hostname to bind to." Enter 0.0.0.0 after host= and remove the leading comment (;).
Let us know if this solves the problem.
73, Howard W6HN