I think I can answer my own post now – for anyone who encounters a similar problem.
I think this happens when you render a project before it’s finished ‘conforming’ all the assets. In other words, in a fit of impatience, you start working on the project while it’s conforming and you render.
Thank you, Ann and Jeff, for coming to my rescue again. I’ll go back to the problem with your tips in mind. This one might take a little more study than the “curly triangle thingy’ in video effects did.
I’m thinking I need to get better aquainted with markers, too?