Someon'es going to tell you to ask this in the Vegas forum, https://www.vegascreativesoftware.info/us/news-forum/, but very sad to see this, it's something earlier version sof Vegas used to do and you'd sort of hope they would have fixed it.  Anyway, what worked for earlier versions was open a version of vegas with just a few secs of footage on the timeline, select render as, should open, close it, then open your project and render should work.