Same issue here, on a Dell laptop with Awesome WM.
Kernel : 5.7.19-2-MANJARO
It has actually been at least a month since that problem appeared already (so it’s not a super recent change in the code or something)
The behaviour is quite weird. If the sound is at 30% on speakers in pavucontrol, and I plug in the headphones, the sound goes to 3% and mute, still on speakers. Then if I unplug the headphones without doing anything, it goes back to 31% (it’s -30.75dB so I suppose it rounds a value) but stays muted.
If, when I plug in the headphones, I manually switch to the headphones in pavucontrol they go back to their old value and are directly unmuted. Then when I unplug them again, pavucontrol switches to speakers, but with muted sound at 3%, which I guess is the last value it had.
Not sure what would be useful to troubleshoot this, honestly. Also, @mrw01f, do you have the same behaviour?