Thank you for looking into this so fast!

Okay I disabled the service to get back to the state I was in:

$ sudo systemctl disable alsa-fix.service
Removed
symlink /etc/systemd/system/multi-user.target.wants/alsa-fix.service.

Btw I did a fast test before that and after resume from hibernate the
workaround doesn't seem to work anymore (only after reboot probably)...
I am still learning; am on Debian since 3 weeks.

then I did a --reinstall of alsa-base/utils & libasound2 for pristine
installation of those 

$ sudo apt-get install --reinstall alsa-base alsa-utils libasound2


I checked my $home/ folder for hidden files using 
$ls -a 
but there is no .asoundrc file there

I made a collection of screenshots of alsamixer and pulseaudio settings
for you; I hope they can help to resolve the issue. First two
screenshots are xterm output.

As you can see the channels are correctly auto-muted when I switch from
speaker to headphone jack, but there's simply no audio coming out of
that jack. Even pulseaudio shows a sound ping when I test headphone
configuration (last screenshot). I also tried muting and unmuting in
pulseaudio settings and switching to Analog Stereo configuration, no
deal.


I hope I'm able to help you fixing this!