Sound card works with ALSA, but not showing in volume mixer

Question

After a system upgrade I noticed I had no sound. In the volume mixer I see that my integrated sound card is not shown, while another one (HDMI) is.

I managed to find that the device name is CARD=MID using aplay -L and I can indeed hear sound when I perform this:

$ for dev in `aplay -L | grep "CARD=MID"`; do aplay -D $dev /usr/share/sounds/alsa/Front_Right.wav 2> /dev/null && echo $dev; done
default:CARD=MID
sysdefault:CARD=MID

I can also hear sound with speaker-test, without any arguments.

In alsamixer the card is as well shown, it appears as the default one (HDA Intel MID), and I can adjust the volume from there when I play sound with aplay or speaker-test.

In order to get the sound card work in the system, I stopped pulseaudio and removed the local configuration files at ~/.config/pulse/, but nothing changed on restart.

I think that the system upgrade could have left some sound configuration in a broken state, but I don't know where to look into.

Edit:

I attach the output of lsof -n /dev/snd/* in some situations.

With pulseaudio stopped:

$ lsof -n /dev/snd/*
$

with pulseaudio running:

$ lsof -n /dev/snd/*
COMMAND    PID    USER   FD   TYPE DEVICE SIZE/OFF  NODE NAME
pulseaudi 3463 etuardu   16u   CHR 116,14      0t0 13058 /dev/snd/controlC1
pulseaudi 3463 etuardu   23u   CHR 116,14      0t0 13058 /dev/snd/controlC1
$

while playing sound with speaker-test:

$ lsof -n /dev/snd/*
COMMAND    PID    USER   FD   TYPE DEVICE SIZE/OFF  NODE NAME
pulseaudi 3463 etuardu   16u   CHR 116,14      0t0 13058 /dev/snd/controlC1
pulseaudi 3463 etuardu   23u   CHR 116,14      0t0 13058 /dev/snd/controlC1
speaker-t 3481 etuardu  mem    CHR  116,2          13523 /dev/snd/pcmC0D0p
speaker-t 3481 etuardu    3r   CHR 116,33      0t0  2850 /dev/snd/timer
speaker-t 3481 etuardu    4u   CHR  116,2      0t0 13523 /dev/snd/pcmC0D0p
speaker-t 3481 etuardu    5u   CHR  116,5      0t0 11209 /dev/snd/controlC0
$