Does this occur when plugin support is disabled (uncheck the "Enable Plugin Support" option on the "General" tab of the VoiceAttack options window and restart VoiceAttack)?
Have you tried creating an empty profile and just having VoiceAttack running in the background?
Just so we're clear, if VoiceAttack is not running, but circumstances are the same otherwise (E.G. in VR running Elite:Dangerous or DCS), this does not occur?
VoiceAttack doesn't shut down Windows unless it's been set up to do so, E.G. through a command containing the "Windows Miscellaneous Functions" action set to the "Shutdown PC" option.
There are also key combinations that can result in Windows shutting down, E.G. Win-D, followed by Alt-F4, followed by the Enter key.
I'll assume you didn't get a look at the log on VoiceAttack's main window to check whether and which commands were executed before the shutdown commenced, especially considering you'd have a VR headset on.