Last night I spent one of those exploratory hours previewing most of the included soft synths while looking for a certain sound. 
Under VST3 there is just one synth Prologue. When I tried to open it, a box popped up asking if I wanted this unknown program to run and then Sonar crashed before I responded.   
I  set Sonar to always run as administrator so it's not that unless that reverts during an update. 
I don't think I need this synth but just wondering as I have not had a crash in a long time. 
 

Never heard of Prologue.
It's not part of Sonar AFAIK

Google says that is a Cubase synth, perhaps proprietary?

Duh! Shows you how much I use Cubase! Thanks. It's always been there so I assumed it was Sonar.