Did you happen to run across this French Ubuntu forum where they recommended
you blacklist the HDMI sound output on the system?
https://forum.ubuntu-fr.org/viewtopic.php?pid=21874250#p21874250
If I translate the French instructions for doing the blacklist, I get the
following:
1. the HDMI port is mistakenly considered a sound card.
To avoid it you have to create a file in the folder (under root):
/etc/modprobe.d
naming itself:
blacklist_snd_hdmi_lpe_audio. conf
containing a single line:
snd_hdmi_lpe_audio
