@chadmaestro
Thanks, you’re on the right track! This indeed solves the error. I thought version 2.0 would remain backward-compatible but maybe not after all.
In any case it has helped me sort things out because I was only keeping the NG shortcode in there for later options – I use Justified Image Grid and Lightbox Evolution to display my thumbs and galleries; NG is only present in the background.
So I removed the NG shortcode altogether and error is gone.