This does look like a bug. As you noticed, VirtualBoxVM detects this crash and saves some diagnostic information in the corresponding log file. However, it isn't giving a lot of hints.
The best way to help some developer work on this issue would be to enable MiniDumps as described on https://www.virtualbox.org/wiki/Core_dump#WindowsMiniDumps and provide it (usually doesn't work as an attachment due to its size).
You could try upgrading to VirtualBox 6.1.20, because that has some fixes for the audio functionality. I don't remember that it resolves this symptom, but you could narrow it down yourself before upgrading: try disabling audio for your VM and see if the crash still happens.