virtualbox pulseaudio backend broken after 6.1.24
Filing this just to collect the information in one place.
It was discussed on the mailing list that after updating to virtualbox-6.1.28, VM's couldn't be started because of problems with the audio devices:
Predrag posted in that thread and confirmed that it's the PulseAudio backend that is at fault.
It turns out this issue isn't specific to OI. The FreeBSD folks have the same issue, and they update more frequently so they were able to identify it as a regression introduced in virtualbox 6.1.24: