It seems that they released an update and the issue seems to have been corrected. Thanks for your assistance.
I systematically went through disabling one plugin at a time and the issue seems to be some sort of conflict with LearnDash LMS. I am running v. 1.4.1 of that plugin. As soon as I deactivate it, my menus came back.
Big bummer as I was hoping to use that plugin (and purchased it) to create some online courses. Any suggestions on how to resolve the conflict?