I looked back over this thread and realized that I didn't address your original comments entirely.
Mumble client on the RigPi does need to be connected to the Murmur server on the RigPi.
That client is the one that will route the TX and RX audio to and from the radio to the server.
Then, you talk and listen to the radio via the Mumble client on whatever remote device you are using, such as your iPhone.
The Mumble logs are located in /var/logs/mumble-server where you will find the current file mumble-server.log along with archived logs from the past.
You can look at the current log using cat mumble-server.log
Does the log file point to anything?
And If you are going to make any changes, now is a good time to make that back-up of your microSD.
You might also want to export your wsjt-x logs before making changes.
73 - Mark - K8MHW
'A RigPi Enthusiast!' - I am not otherwise affiliated with MFJ or RigPi