Normally when you have a multicam video (or any video for that matter) in your timeline, you'll see a yellow bar across the entire length of the timeline showing that there is something that will be output in the final video.
I just finished editing a project, closed Premiere, then reopened, and I noticed that parts of the video were black screens. These lined up to those that didn't have yellow bars on top:
How do I get the bars back on top?