Freepbx 10.13.66-11 suddenly no audio

Our freepbx has suddenly stopped passing audio - even from our extension to extension there is nothing. Our extensions are all on the same Layer 2 network as our freepbx server.
I’ve checked no one has plugged anything new into the network and rebooted our switches, phones and freepbx server.
I’d add a log but the webpage won’t allow me…