This started to happen after applying the 5.5 series backports.
If I let the system boot normally there is no sound. KDE will show only "dummy output". If I go to the shell and run "aplay -l" it will say not sound cards found. Alsa drivers are not loaded.
Now if I boot into recovery mode, select root shell, and run "aplay -l" the sound card is listed and the drivers are loaded. If I then exit the shell and resume normal boot into the desktop the sound will work fine.
There is apparently something in the desktop boot sequence that is blocking the Alsa driver from being loaded.
I found other threads discussing similar problems caused by settings between pam, systemd, and sddm, however the solutions in those cases didn't apply (ie they had missing settings that are OK on my system).
If I let the system boot normally there is no sound. KDE will show only "dummy output". If I go to the shell and run "aplay -l" it will say not sound cards found. Alsa drivers are not loaded.
Now if I boot into recovery mode, select root shell, and run "aplay -l" the sound card is listed and the drivers are loaded. If I then exit the shell and resume normal boot into the desktop the sound will work fine.
There is apparently something in the desktop boot sequence that is blocking the Alsa driver from being loaded.
I found other threads discussing similar problems caused by settings between pam, systemd, and sddm, however the solutions in those cases didn't apply (ie they had missing settings that are OK on my system).