After days of diagnosing plugins, etc. to see what may have been causing Visual Composer to disappear from the edit pages (and Yoast SEO in some cases as well), I FINALLY found that the WPMU Video Tutorial plugin was actually the culprit in all four cases. I've deleted the video plugin from all of my installs so I can't show the conflict live, but you'll quickly see what happens if when you install the videos plugin with any theme that uses the Visual Composer plugin. Just a head's up as I bet it's causing some other users some heartache as well. It's the very last plugin I thought would ever create a conflict so I bet others haven't even considered trying to deactivate it. Thanks.