It was suggested I report this issue here:
I have been successfully using the Mumble Snap for a few months now on two separate machines using Ubuntu 20.04. As of the last 48 (or so) hours, both machines no longer can access the input device. Machine #1 is using a Yeti Mic via USB, and Machine #2 is using Razer gaming headsets through an analog port. Both worked fine, both stopped working at around the same time. I assume, there was a snap update that might have broke something.
I have since installed the APT version of Mumble from the Ubuntu repositories and that particular version discovers my input devices perfectly.
If more information would be helpful, please let me know. Happy to get what might be required. I’d rather be using the snap version.