Wrong default audio device

I had the same problem after upgrading from Ubuntu 19.04 to 19.10. What you have to do is go to

 /etc/pulse/default.pa

comment out

.ifexists module-switch-on-connect.so
load-module module-switch-on-connect
.endif

and reboot.

I hope it helps!

I have the same exact issue, fix does work but it is not the correct fix IMO When doing this you have now also commented out automatic connection for bluetooth headsets etc I believe

The section commented is

#Use hot-plugged devices like Bluetooth or USB automatically (LP: #1702794)
#Commented after upgrade from 19.04 to stop HDMI which has no speakers attached from stealing audio from Line out
#.ifexists module-switch-on-connect.so
#load-module module-switch-on-connect
#.endif

That LP 1702974 link is https://bugs.launchpad.net/ubuntu/+source/pulseaudio/+bug/1702794

And it says

This way once a user pairs & connects a bluetooth speaker device pulseaudio will auto switch to it. As it stands now users have to open sound settings & switch manually. It's bad enough that auto discover & connect don't work, (can be scripted thru bluetoothctl), no sense adding to frustration

Looks like we want that but dont want HDMI monitors that can carry audio on the link but have no actual speaker attached to take the channel.