I was advised to upgrade to Vegas 21 as Vegas 18 is a legacy version and they can’t do anymore to support it.I’ve bought Vegas 21 and i don’t get the crashing problem on rendering. The only issue I have with Vegas 21 is that it takes a long while to load a project. I think it’s the MXF files that cause that.
The extra loading time you notice may be a result of proxy files being built. If so, it should only happen once, look at the progress indicator lower left.