On first launch system sounds shown at 0% volume but really are not

[Nick]

Fresh installation + updates of 20.04. The system sounds (e.g. plugging in charger) volume is shown to be at 0% volume but they are still playing. This is worked around by dragging the slider up then back to 0. I would have expected it to be at around 20% volume based on the loudness of the sounds.

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: gnome-control-center 1:3.36.3-0ubuntu1
ProcVersionSignature: Ubuntu 5.4.0-40.44-generic 5.4.44
Uname: Linux 5.4.0-40-generic x86_64
NonfreeKernelModules: wl
ApportVersion: 2.20.11-0ubuntu27.3
Architecture: amd64
CasperMD5CheckResult: skip
CurrentDesktop: ubuntu:GNOME
Date: Tue Jul 14 19:29:18 2020
InstallationDate: Installed on 2020-07-13 (0 days ago)
InstallationMedia: Ubuntu 20.04 LTS "Focal Fossa" - Release amd64 (20200423)
ProcEnviron:
 LANGUAGE=en_AU:en
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_AU.UTF-8
 SHELL=/bin/bash
SourcePackage: gnome-control-center
UpgradeStatus: No upgrade log present (probably fresh install)