This seemed to do the trick, thanks.
I purged MongoDB and Node.js then reinstalled both, but v10 of Node.js, which meant all plugins updated properly when reinstalling Adapt authoring tool.
However, I now have an issue with MongoDB (I think). I cannot save courses or upload media to library. When I create a new course and click on Save, the wheel spins, says Saving and just doesn't stop. Then I cannot exit screen or even log out of authoring tool (see my most recent discussion - hope you/someone could help).