Not exporting duplicated image files

Hi! I’m a recent convert from Lightroom 6 to Lightroom CC and am having problems exporting images that I have made a duplicate of. When I edit a gallery I was accustomed to “creating a virtual copy” to make copies and creating black and white images from my colored edits. From my research I’ve found that ‘virtual copies’ no longer exist and now are just ‘duplicates’ (because CC charges for image storage).

The problem I’m having: when I export a full gallery it will not export the duplicated file nor the original file and gives me a “this file is not found” error. BUT when I choose only the original and duplicate file (and not in a batch) it will export them!! This is driving me nuts!! Anyone have any ideas or tips???