Thanks to everyone, for your replies!
Just read the thread - thanks, Daniel - and found that eliminating a comma from my Dorico filename fixed the problem. Also saw that dragging & dropping the file onto the Hub also did the trick.
I understand, from the "No such file or directory" - #15 by dan_kreider thread, that there may be multiple behind-the-scenes Dorico operations at work that cause this, so I don’t imagine that it would be an easy thing to resolve; however, is such a fix still on the horizon?
Thanks again!